In what I think of as engineering terms: an agent is a long running service that invokes LLMs during its execution. In contrast to an LLM driven application where the primary function is synchronous with the end user (like chatGPT). There's a blurry line there but that's how I think about it.

AutoGPT and BabyAGI are probably the two most well known examples so far.

A significant struggle when building these types of applications is understanding and debugging behavior many execution steps deep. This tries to assist with that by giving a framework for structuring the way your agent runs.

Maybe a similar concept is breaking out a web application into services, or individual route handlers, rather than implementing everything as one massive loop that responds to events.