My definition for an Agent is "a marketing term for long running LLM Chat sessions that has increased access to use your computer to complete tasks it cannot otherwise do by itself".
That's my attempt at a universal definition for technical and non-technical users. How does it compare?
Well, my reference for a commonly used incorrect definition is “anything that involves using an LLM” so yours is better than that.
But the elements that I think are necessary are 1) goal-oriented processing, 2) ability to use tools, 3) ability to iterate and self-correct. Along with that typically comes 4) self-talk or other hidden context during execution and 5) support for defined personas beyond system or user prompts.
That’s off the top of my head, probably not complete/correct, and definitely meant to be more technical than a non-tech person would need.