A piece of AI software that automatically performs a task on a human's behalf, or even on the behalf of another piece of AI software, so together they accomplish a useful task for a person somewhere. They are capable of independent action in dynamic, unpredictable environments. "Autonomous agent" is a trendy term that is sometimes reserved for AI software used in conjunction with the Internet (for example, AI software that acts as your assistance in intelligently managing your e-mail).
Autonomous agents present the best hope from gaining additional utility from computing facilities. Over the past few years the term "agent" has been used very loosely. Our definition of a software agent is: "an intelligent software application with the authorization and capability to sense its environment and work in a goal directed manner." Generally, the term "agent" implies "intelligence", meaning the level of complexity of the tasks involved approaches that which would previously have required human intervention.

This definition is in context to Artificial Intelligence. See more contextual defintions for Autonomous Agents.