An AI agent is a computer helper, powered by artificial intelligence, that can carry out a task made of many steps largely on its own — you describe the goal in plain words, and it plans and performs the steps needed to reach it.
The difference from an ordinary program is that you do not have to spell out every single click. A normal program follows a fixed recipe, while an agent can work out the recipe as it goes, check its own work and adjust. A simple picture: instead of a calculator that only does what each button says, it is more like a capable assistant you can ask to “gather these numbers, put them in order and send me the result,” and it handles the pieces itself.
In practice this speeds up work such as writing and checking a website’s code, or connecting different services together. The person still sets the goal, reviews the result and stays responsible for the quality — the agent is a fast helper, not a replacement for human judgement.