An AI agent is a software system that can pursue a goal with a degree of independence. It observes its environment, decides what to do, takes actions using tools such as web search, apps, or code, checks the results, and keeps going until the job is done or it needs human input. Most modern agents are built on large language models, which give them the ability to understand instructions, plan, and reason in plain language.
Here is the difference in practice. Ask a regular chatbot "What are some good hotels in Lisbon?" and it gives you a list. Ask an AI agent to "find a hotel in Lisbon under $150 a night near the old town for May 10 to 13, and put the best three options in a spreadsheet," and it can search booking sites, compare prices and locations, filter the results, and create the spreadsheet, checking its own work along the way.