Terms are grouped by what they describe: the idea, the surfaces where shoppers meet agents, the plumbing under them, and the measurement. Each entry says where the definition comes from. Where AC Brief uses a term its own way, the entry says so.
The idea
Agentic commerce. Selling and buying in which AI agents do part of the work: finding products, comparing them, answering questions, and increasingly placing the order. On the merchant side the term also covers AI agents that run store operations. See What is agentic commerce? for the operator view.
Shopping agent (AI agent). Software that acts for a shopper inside an assistant or a browser: it can search, compare, add to cart and, with permission, pay. Meta’s Muse, Perplexity’s Comet browser and the agents built into Google’s AI Mode and Microsoft Copilot are examples. Agents differ in whether they ask before buying; Muse does.
Agentic storefront. Shopify’s name for the version of a store that an AI channel can read and, where supported, buy from, controlled under Sales channels › Agentic. Full explainer: What is an agentic storefront?
Agentic checkout. An agent completing a purchase, either natively inside an assistant or by operating the merchant’s own checkout. Full explainer: Agentic checkout, explained.
Direct checkout. Shopify’s per-channel switch that lets a sale close inside the assistant instead of on the merchant’s site. On by default for eligible stores where the channel supports it.
The AI shelf. AC Brief’s own term for the set of places where an assistant shows products to a shopper. Being “on the shelf” means the assistant can find, trust and show your product. Our free AI Shelf Checklist scores a store against it.
Surfaces
AI Mode and Gemini (Google). Google’s conversational search and its assistant. Since September 2026, eligible US Shopify stores can be bought from inside both, on by default and still rolling out. Google also tests buying from other retailers, such as a Flipkart Buy button in India (reported).
AI Overviews (Google). The AI summary at the top of some Google results. It can cite and link merchants but does not sell. Google says its AI features need no special files or markup beyond normal indexing.
Muse (Meta). Meta’s personal AI agent, launched in the US on 8 September 2026. It can browse and buy on a shopper’s behalf, asks before paying, and pays through Stripe Link one-time cards. On 24 September Meta announced Walmart, Best Buy, Sephora, Wayfair and six more retailers plus Shop Pay and PayPal, with no dates. Muse for Small Business, launched 29 September in the US and Canada, is a different product: an agent that connects to a merchant’s Shopify, Klaviyo, Stripe and Meta ad accounts and, Meta says, publishes, sends or spends nothing without approval.
Copilot Checkout (Microsoft). Buying inside Microsoft Copilot, for US shoppers and English-language merchants selling in US dollars. Shopify stores are enrolled automatically with controls in the Shopify admin.
ChatGPT Ads and Sponsored Agents (OpenAI). Paid placement inside ChatGPT, available in more than 60 countries for Free and Go users. US Shopify merchants can run ads through a free Shopify app that reads Shopify Catalog; during the beta, products uploaded for ads do not appear in organic answers. Sponsored Agents, in a limited alpha, let a shopper chat with a business’s own labelled agent after clicking its ad.
Instant Checkout (ChatGPT). OpenAI’s name, in September 2025, for buying inside ChatGPT, launched with US Etsy sellers and built on the Agentic Commerce Protocol below. AC Brief’s 2026 coverage has not yet covered its current scope; check OpenAI’s documentation.
Ask YouTube. YouTube’s assistant. Since September 2026 a review search can return grouped videos with a comparison table of product attributes. It answers from creator videos, not from your product page.
Seller Assistant (Amazon). Amazon’s AI helper for sellers. Since September 2026 it can run standing tasks, in recommend or act mode, with the seller approving actions and an audit trail. Related: Buy with Prime and MCF (Multi-Channel Fulfillment), which let US merchants using Amazon’s fulfilment offer Prime delivery on their own site through a Shopify app.
Plumbing
Shopify Catalog. The product data Shopify shares with AI channels. With Allow Shopify to manage for me on, every channel gets it; switching catalog access off entirely can take up to 7 days to take effect, Shopify says.
WebMCP. An emerging web standard that lets a page expose “tools” an agent in the browser can call. Shopify ships WebMCP tools on every Liquid store: storefront and cart since 5 August 2026, checkout since 28 September (get_checkout, update_checkout, complete_checkout, navigate_to_storefront). Only Chromium browsers support it so far.
Web Bot Auth. A way for an agent to sign its requests so a site can tell a legitimate agent from a scraper. Shopify tells agents to use it or risk its bot protection.
llms.txt and agents.md. Plain-text files at a site’s root that describe the site to AI systems. Shopify stores serve editable versions of both. Google says its AI features do not need them. AC Brief publishes its own at /llms.txt.
ACP (Agentic Commerce Protocol). An open specification from OpenAI and Stripe, published 29 September 2025, for how an agent sends a merchant an order and payment. Not to be confused with Postscript’s “Agentic Context Platform”, which shares the initials.
UCP checkout (Google). Google’s checkout program for merchants in Merchant Center, documented for select merchants with an interest form. Shopify’s Google channel appears to sit on top of it, but Google’s help page does not mention automatic Shopify enrolment, so AC Brief marks the Shopify switch-on as reported.
3-D Secure. The extra authentication step some card payments require. Shopify’s agent tools hand control back to the shopper when it appears; an agent cannot complete it.
Server-side events. Order events Shopify sends from its servers rather than from the shopper’s browser. Inside an assistant’s checkout these are the only events that fire; Google Analytics and pixels do not.
One-page and three-page checkout. Shopify’s two checkout layouts, set under Settings › Checkout. Browser agents can complete the three-page version only when the shopper uses Shop Pay.
Human approval gate. A step in an AI workflow where a person must approve before anything publishes, sends, spends or ships. Meta’s Muse for Small Business, Amazon’s Seller Assistant and Noibu’s store-fix workflow all describe one. AC Brief treats a missing gate as a reason to skip a tool.
Measurement
Agentic report (Shopify). Per-channel sales and orders under Sales channels › Agentic. The place to count assistant orders, since GA cannot see them.
Search preview (Shopify). A view of how products might appear in each AI channel, with a listing-quality meter for description, images, reviews, variants and policies. Channels re-rank results, so it is a guide, not a ranking.
AI performance insights (Merchant Center). Google’s report comparing a brand’s share of voice across surfaces including AI Mode and AI Overviews. Available in Australia, Canada, India, New Zealand and the US as of September 2026.
Generative AI performance report (Search Console). Impressions in AI Overviews and AI Mode by page, country and device, rolled out to all sites worldwide on 31 August 2026. It shows no clicks.
AI traffic (Adobe’s definition). Visits to a retail site from a link in an AI service. Adobe forecasts a 130% year-on-year rise for US retail between 1 November and 31 December 2026, and reported in August that such visits converted 60% better than other traffic in July. Clicks, not agent purchases.
Reported (AC Brief’s usage). A claim that rests on secondary reporting only, with no primary source from the company involved. Verified means a company newsroom, help centre, changelog or official documentation says it.
Missing a term? Reply to any issue and we will add it. Definitions are read from the platforms’ documentation and announcements; nothing here was tested on a live store by AC Brief.