An AI agent is an autonomous system that uses a large language model as its reasoning core, combined with tools and memory, to plan and execute tasks with minimal human intervention. Agents can use tools like web search, code execution, file access, and API calls to gather information and take real-world actions. Unlike a simple chatbot that responds to individual queries, an agent manages multi-step workflows — breaking a complex goal into subtasks, executing them sequentially, and adapting based on results.