An AI agent is software that can take autonomous actions to accomplish a goal — not just answer questions, but actually DO things. A chatbot answers when you ask. An agent plans steps, uses tools (search the web, read files, call APIs, send emails), and works toward a goal with minimal human intervention. For example, an AI agent might research a topic, draft a report, fact-check it against sources, and email the final version — all from a single instruction. The agent paradigm is the biggest shift in AI since large language models. It moves AI from a tool you use to a worker that acts on your behalf.