What do the terms in agentic commerce mean?
This glossary defines the protocols, metrics and techniques that come up when a shop prepares for AI shopping agents. Each definition stands on its own and links to the guide that explains it in depth, so you can send a colleague a single term rather than a whole article.
- Agent Payments Protocol (AP2)
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An open protocol announced by Google on 16 September 2025 with more than 60 organisations, and donated to the FIDO Alliance on 28 April 2026, that records what a person authorised an agent to buy through cryptographically signed mandates. Version 0.2 adds payments completed while the person is not present.
- Agent2Agent (A2A)
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An open protocol through which AI agents exchange messages and tasks with other agents. Google states that UCP and AP2 are compatible with it, so a merchant rarely implements it directly.
- Agentic checkout
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A checkout an AI agent completes for a person through a protocol such as UCP or ACP, passing the order and a payment credential to the merchant, who stays the seller of record. It launched in the United States first.
- Agentic commerce
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Buying done by an AI agent on a person's behalf, from searching and comparing products to filling a basket and, where the merchant and the channel allow it, paying.
- Agentic Commerce Protocol (ACP)
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An open protocol published by OpenAI and Stripe in September 2025, under the Apache 2.0 licence, that lets ChatGPT send an order and a delegated payment token to a merchant, who remains merchant of record. OpenAI moved Instant Checkout into apps inside ChatGPT in March 2026 and kept ACP as the link to merchants.
- Answer capsule
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A 40 to 60 word answer placed directly under a question heading, written to stand on its own so an assistant can retrieve and quote it without the rest of the page.
- Answer Engine Optimization (AEO)
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Work aimed at being the source an AI assistant or a search feature quotes when it answers a question directly. Often used interchangeably with Generative Engine Optimization.
- Cart mandate
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In AP2 as described at launch, a signed record that binds a person's approval to one specific basket and amount, so the merchant can verify the agent is paying for exactly what was approved.
- Context rot
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The decline in a model's reasoning as its context fills with long or noisy text, for example after many tool calls. In agent checkout it shows up as abandoned carts and invented parameters.
- Context window
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The limited amount of text a model reads before it writes an answer. Retrieved passages compete for this space, and only what is placed in it can be cited.
- Direct Agent Conversion Tracking (DACT)
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Autobasket's method of sending agent orders to GA4 from the server, tagged with the assistant and protocol, so they appear as their own channel instead of as direct or unassigned traffic.
- Generative Engine Optimization (GEO)
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Work that raises how often generative engines such as ChatGPT, Perplexity, Claude and Google AI Overviews retrieve, cite and recommend a source. The term comes from a Princeton-led paper presented at KDD 2024, which measured gains of 30 to 40% from adding sources, quotations and statistics.
- GTIN
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The Global Trade Item Number behind a product barcode, in 8, 12, 13 or 14 digits. Declared in structured data and feeds, it lets an agent confirm that two listings describe the same item. Google Merchant Center lists it as recommended, and OpenAI's product feed as optional.
- Human Not Present
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An agent payment completed later, without the person confirming at that moment, under limits they signed in advance in an intent mandate. AP2 added it in version 0.2 in April 2026.
- identifier_exists
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A product feed attribute set to no when a product has no GTIN or MPN, such as an own-brand item. In OpenAI's Google-compatible feed format it lifts the requirement for a GTIN or MPN.
- Intent mandate
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In AP2, a signed record of a person's instruction and its limits, such as items, budget and timing, that authorises an agent to buy within them, for example a monthly reorder up to a set amount.
- JSON-LD
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A format for structured data placed in a script tag on a web page. Using the Schema.org vocabulary, it states a product, its offer and its seller as fields an agent can read exactly.
- llms.txt
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A Markdown file at the root of a site, proposed by Jeremy Howard in September 2024, that lists the pages an AI system should read with one line on each. Google states that Search ignores it and that no such file is needed for AI Overviews.
- Markdown mirror
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A plain-text copy of a web page at the same address with .md added, without layout or scripts, so an agent spends its context on content rather than markup.
- Model Context Protocol (MCP)
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An open protocol, released by Anthropic in November 2024 and stewarded by the Linux Foundation's Agentic AI Foundation since December 2025, through which AI assistants discover and call outside tools, such as a shop's catalogue search, over JSON-RPC 2.0.
- Product feed
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A file or API a merchant sends to a shopping channel with one row per product and fields such as price, availability, brand and GTIN. OpenAI publishes a feed specification for ChatGPT, and Google Merchant Center takes its own.
- ProductGroup
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The Schema.org type for a product sold in variants, such as sizes or colours. It lists each variant with hasVariant and states which attributes change with variesBy, so an agent can confirm the exact variant is in stock.
- Query fan-out
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A technique Google says AI Overviews and AI Mode may use: one question is split into several related searches across subtopics and data sources, and the answer is assembled from the results.
- Retrieval-augmented generation (RAG)
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The pattern most AI assistants use for current questions: retrieve relevant passages from the web or an index, place them in the context window, then write the answer from them.
- Universal Commerce Protocol (UCP)
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An open checkout standard launched by Google on 11 January 2026, co-developed with Shopify, Etsy, Wayfair, Target and Walmart, through which agents complete purchases with any merchant over REST, MCP, AP2 or A2A. Checkout started in AI Mode and the Gemini app for eligible US retailers.
- Verifiable Intent
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A record of user-authorised agent actions, co-developed with Mastercard and compatible with AP2, donated to the FIDO Alliance together with AP2 in April 2026.
- x402
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An open specification for paying per request over HTTP, using the 402 Payment Required status code and stablecoins such as USDC. Google launched an A2A x402 extension with Coinbase alongside AP2.
Turn the vocabulary into a fix list
The readiness check reports on your own product page in the same terms, with the evidence it found and the change that fixes each item.