Anything perceives its environment by sensors and acts upon an environment by effectors are known as Agent. Agent includes Robots, Programs, and Humans etc.
In artificial intelligence, an agent refers to any entity that perceives its environment through sensors and acts upon that environment through actuators, with the goal of achieving certain objectives. The concept of an agent can be applied to a wide range of systems, from simple automated programs to complex autonomous robots.
A more technical definition of an agent is provided by Russell and Norvig in their book “Artificial Intelligence: A Modern Approach”, where they define an agent as “anything that can be viewed as perceiving its environment through sensors and acting upon that environment through actuators.”
Agents can vary greatly in complexity and capability. They can be as simple as a basic program designed to automatically respond to specific inputs, or as complex as a sophisticated AI system capable of learning, reasoning, and making decisions in dynamic environments. Examples of agents include chatbots, self-driving cars, recommendation systems, and game-playing AI programs.