The Agent Glossary

Plain-English definitions for the AI-agent era — agentic commerce, the Model Context Protocol, GEO and agent payments. Every term answered in one sentence, then explained.

AI agents & concepts

AI agentRAG (Retrieval-Augmented Generation)Function calling (tool calling)A2A (Agent2Agent protocol)Prompt injectionProof of personhood

Agentic commerce

Agentic commerceAgentic Commerce Protocol (ACP)Universal Commerce Protocol (UCP)AI shopping agentChatGPT ShoppingAgentic checkout

AI visibility (GEO/AEO)

Citation shareGenerative Engine Optimization (GEO)Answer Engine Optimization (AEO)llms.txtagents.mdAI OverviewsZero-click searchStructured data (schema markup)

Model Context Protocol

Model Context Protocol (MCP)MCP serverStreamable HTTP (MCP transport)MCP toolMCP Registry

Agent payments

x402AP2 (Agent Payments Protocol)Agentic paymentsx402 facilitatorHTTP 402 (Payment Required)EIP-3009 (transferWithAuthorization)Monetization Gateway (Cloudflare)Pay per crawlAgent wallet (programmable wallet)Shared Payment Token (SPT)Mandate (AP2)

Ready to act on any of these?

Free tools for the agentic era.

Scan a store   Scan an MCP server