Plugin.

A plugin is an add-on you install to give your agent new abilities. Where a single Skills teaches it one task, a plugin usually bundles a whole kit in one install, often an MCP (Model Context Protocol) plus a set of skills together.

Instead of wiring up a Shopify connection and then hunting down five separate skills for it, you install one Shopify plugin and your AI can run your store for you. One install, and everything shows up.

Anthropic ships free open-source ones for legal, finance, marketing, sales, and support. You drop one in and the agent knows how to do that whole category of work.

Keep one thing in mind. A plugin is someone else's code running inside your agent with your permissions, and that's exactly what Prompt injection rides in on. Treat plugins like any app you install on your phone. Use ones from sources you trust, and if you're not sure, scan it before you let it run.