GST Glossary: 45+ GST Terms and Abbreviations Explained (2026)

GST conversations run on abbreviations — GSTR-3B, RCM, LUT, QRMP — and each one hides a real task with a real due date. This glossary defines the terms GST-registered businesses meet in 2026, in plain English, grouped the way you encounter them: the taxes themselves, registration and returns, documents and identifiers, then payments, credit and enforcement. Rate references reflect the GST 2.0 structure in force since 22 September 2025.

The taxes and core concepts

CGST

Central GST, charged on supplies within the same state — the Centre’s half of an intra-state tax. It appears on every tax invoice as a separate line from SGST or UTGST.

SGST

State GST — the state government’s half of the tax on intra-state supplies, collected by the state where the supply is consumed. Rates of CGST and SGST mirror each other on the same invoice.

UTGST

Union Territory GST — SGST’s counterpart in union territories without their own legislatures. Delhi and Puducherry levy SGST instead, because they have elected assemblies.

IGST

Integrated GST on inter-state supplies and imports, collected by the Centre and apportioned to the destination state. One line of IGST replaces the CGST-plus-SGST pair whenever place of supply crosses a border.

Composite Supply

A bundle supplied naturally together with one principal item — say, a laptop with its charger — taxed at the principal item’s rate. You cannot split the tax across the parts of the bundle.

Mixed Supply

A bundle of items that could be sold separately, offered for one price — say, a festival hamper of dry fruits and sweets. The whole bundle is taxed at the highest-rated item’s rate.

Nil-Rated

Goods listed in the rate schedule at zero percent — the rate exists, but it is nil, so no input tax credit is available on inputs used to make them. Do not confuse this with exempt supplies, which are pulled out of tax by notification.

Exempt

Supplies notified as tax-free — for example, fresh food items, education or health services. No output tax is charged and no input credit is available for making such supplies.

Zero-Rated

Exports and supplies to SEZs, taxed at zero with the input credit refundable. You supply either without paying IGST under an LUT, or with payment of IGST followed by a refund claim.

Place of Supply

The location that decides which tax applies — CGST plus SGST within a state, IGST across states — and which government keeps the revenue. It is a legal definition based on delivery and use, not merely the shipping address.

Time of Supply

The point at which liability crystallises — generally the earlier of the invoice date or advance receipt. It fixes the tax period and the return in which the tax must be paid.

RCM (Reverse Charge Mechanism)

The arrangement where the recipient, not the supplier, pays GST on notified supplies — goods transport agency services, legal services from advocates and imports among them. RCM tax is paid in cash, and the same recipient can usually claim its credit.

Section 9(5) Supply

Notified services — such as app-based passenger transport, restaurant service through platforms and housekeeping — where the e-commerce operator, not the individual driver or worker, is deemed liable to pay the tax. The platform reports and discharges this tax itself.

Registration, returns and taxpayer profiles

AATO

Aggregate Annual Turnover — your pan-India turnover number that decides eligibility for the composition scheme, QRMP, e-invoicing and several other thresholds. It is computed for the preceding financial year.

B2B

Supplies to registered businesses, reported invoice-wise with the buyer’s GSTIN in GSTR-1. These documents flow into the buyer’s GSTR-2B, so verify the buyer’s GSTIN with a GST number verification check before invoicing.

B2C

Sales to unregistered consumers, reported state-wise in consolidated tables. Inter-state B2C invoices above ₹2.5 lakh get separate large-invoice reporting; the rest go into small-value B2C tables.

Composition Scheme

A flat-rate scheme for small suppliers — turnover up to ₹1.5 crore (₹75 lakh in special category states) — paying a fixed percentage of turnover, with no input credit and no inter-state outward supplies. Composition dealers issue a Bill of Supply instead of a tax invoice, and file CMP-08 plus GSTR-4.

CASO

Computer Assisted Scrutiny Operation — the GSTN analytics engine that compares returns, e-invoices and e-way bills to flag anomalies for the department. Persistent mismatches with your suppliers are a common trigger for follow-up.

QRMP

Quarterly Return, Monthly Payment — the scheme for taxpayers up to ₹5 crore AATO that allows quarterly GSTR-1 and GSTR-3B while depositing tax monthly through PMT-06, typically 35% of the previous quarter’s cash liability.

IFF (Invoice Furnishing Facility)

The optional monthly upload for QRMP taxpayers in the first two months of a quarter, capped at ₹50 lakh of documents per month. It lets your B2B buyers claim credit without waiting for the quarter to close.

GSTR-1

The outward-supply statement — invoice-wise B2B detail plus consolidated B2C tables — filed monthly by the 11th, or by the 13th of the month after the quarter under QRMP. Everything your buyers claim flows from this return.

GSTR-2A

A dynamic, read-only view of supplies your suppliers have reported against your GSTIN, updating as they file. Useful for chasing defaulting suppliers, but credit is now claimed against GSTR-2B.

GSTR-2B

The static monthly ITC statement auto-generated on the 14th, splitting input credit into available and not-available buckets. Match your books to GSTR-2B before filing GSTR-3B.

GSTR-3B

The summary return where you self-declare outward supplies and ITC claimed, and pay the net tax — monthly by the 20th, or quarterly by the 22nd or 24th under QRMP depending on your state group. It carries no invoice detail; GSTR-1 does that job.

GSTR-4

The annual return for composition dealers, currently due by 30 June after the financial year — verify the current notification, as this deadline has moved several times.

GSTR-8

The monthly return of e-commerce operators reporting supplies routed through the platform and the TCS collected under Section 52, due by the 10th of the following month.

GSTR-9

The annual return consolidating the year’s GSTR-1 and GSTR-3B filings for regular taxpayers. For FY 2025-26 it is due by 31 December 2026; below the ₹2 crore threshold it has been optional in recent years.

GSTR-9C

The self-certified reconciliation statement filed with GSTR-9 by larger taxpayers, bridging audited books to the returns filed. Certification requirements have been relaxed over the years, so confirm the current format.

IMS (Invoice Management System)

The GSTN portal feature that lets you accept, reject or keep pending each supplier’s document, deciding whether it enters your ITC statement. Used actively, it stops wrong credits from slipping into your return.

Documents, codes and identifiers

HSN

Harmonised System of Nomenclature — the product classification code quoted on invoices. From 1 November 2025, 6-digit HSN is mandatory for taxpayers above ₹5 crore turnover and 4-digit for those between ₹1.5 crore and ₹5 crore; confirm your digits with an HSN code finder.

SAC

Services Accounting Code — the services-side twin of HSN, classifying what you sell when the supply is a service rather than a good. It carries the same reporting discipline as HSN.

UQC

Unit Quantity Code — the standard unit (KGS, PCS, NOS and so on) in which quantity must be reported alongside HSN in e-invoices and GSTR-1, keeping data comparable across taxpayers.

e-Invoice

An invoice reported in a standard machine-readable format to the government system before dispatch, receiving a unique IRN and a signed QR code. Mandatory for businesses above ₹5 crore turnover since August 2023, and voluntary below that.

IRN (Invoice Reference Number)

The 64-character hash that identifies each e-invoice uniquely in the system, generated from the supplier GSTIN and document details. One IRN belongs to exactly one invoice for its lifetime.

IRP (Invoice Registration Portal)

The government-authorised system that validates the e-invoice payload, issues the IRN and returns the signed QR code. NIC’s IRP is the most widely used.

e-Way Bill

The electronic movement document generated before consignments above ₹50 lakh are transported, carrying vehicle and consignment details that officers can verify en route. Validity runs by distance and can be extended before expiry.

Bill of Supply

The document issued where no tax can be charged — by composition dealers or for exempt supplies. It looks like an invoice but must not show a tax column.

Credit Note

The document issued to reduce an earlier tax invoice’s value or tax — for returns, post-sale discounts or excess billing. Report it in GSTR-1 so your output tax and the buyer’s credit adjust together.

Debit Note

The counterpart document that increases a tax invoice’s value or tax — for short-billing, extra quantities or omitted charges. It flows through GSTR-1 the same way as a credit note.

ECO (E-Commerce Operator)

A platform through which goods or services are supplied — marketplaces, ride-hailing apps and food delivery among them. Depending on the supply, an ECO collects TCS under Section 52 or bears the tax itself under Section 9(5).

Payments, credit and enforcement

ITC (Input Tax Credit)

The tax you paid on purchases and expenses, set off against tax on your sales, subject to GSTR-2B matching and the blocked-credit exclusions of Section 17(5). Credit is the cash-flow heart of GST, which is why supplier filings matter so much.

LUT (Letter of Undertaking)

Filed as Form GST RFD-11, it lets exporters ship goods or supply services without paying IGST and still claim refunds of input credit. One LUT covers the whole financial year.

TCS u/s 52

Tax Collected at Source that e-commerce operators collect at up to 1% (0.5% CGST plus 0.5% SGST, or 1% IGST) on net supplies through their platform, reported in GSTR-8. Sellers see it as credit in their electronic cash ledger.

DRC-01

The intimation of tax dues issued before formal demand — an itemised notice of suspected short payment or wrong credit, giving you a chance to reply or pay. Complex DRC-01 replies are best drafted with a GST consultant.

DRC-03

The voluntary payment challan used to deposit admitted dues at any stage — even before a notice — helping close the issue without escalation. Keep the acknowledgement safe; it evidences payment of only the amount specified.

DRC-07

The formal demand order confirming tax, interest and penalty after adjudication. Unpaid DRC-07 dues invite recovery, so respond within the time given or pay.

Key takeaways

• GSTR-2B, not GSTR-2A, is the basis for claiming input tax credit each month.
• AATO drives nearly every threshold — composition, QRMP, e-invoicing and the GSTR-9 requirement.
• GST 2.0, effective 22 September 2025, runs on 5% and 18% slabs with a 40% rate for demerit goods — check item-level rates before invoicing.
• Your buyers’ credit depends on your GSTR-1 accuracy and timeliness, so treat outward reporting as shared infrastructure.

Frequently asked questions

What is the difference between GSTR-2A and GSTR-2B?

GSTR-2A updates continuously as your suppliers file, while GSTR-2B is the frozen monthly statement generated on the 14th. ITC must be claimed with reference to GSTR-2B.

Which return is the payment return?

GSTR-3B — it is the summary return in which you declare output tax, credit and pay the net amount. GSTR-1 carries the invoice-level detail; GSTR-9 is the annual consolidation.

Do small businesses need e-invoicing?

It is mandatory above ₹5 crore aggregate turnover; below that, taxpayers can use it voluntarily through the same IRPs. Check your AATO before the year begins.

What changed under GST 2.0?

From 22 September 2025 the rate structure runs on two main slabs of 5% and 18%, with a 40% rate for demerit goods such as pan masala and luxury cars. Verify your HSN’s current rate with a GST calculator before repricing.

Can I claim ITC if my supplier has not filed?

Not in that month — the credit enters your GSTR-2B only once the supplier reports the invoice. Chase the supplier, and use IMS to accept or keep the document pending until it appears.

Disclaimer: Tax laws change frequently. Verify current rates and deadlines on the official portals (incometax.gov.in, gst.gov.in) or consult a qualified professional before acting.