How this differs from the things it resembles

Four things get compared to this, and the differences are structural rather than a matter of quality. None of the four is worse at what it is for.

Against a chatbot

A chatbot exists for the length of a conversation. An agent here is standing: it holds a brief, accrues a run history, owns items on a board, and is still there on Monday having done things while you were not watching. The difference shows up in the second week, when you want to know what it did on Thursday.

Against an automation builder

A canvas of boxes and arrows does the same thing every time, which is exactly right for a deterministic process and exactly wrong for “this supplier replied with something ambiguous”. Agents are briefed in sentences and bounded by settings rather than drawn, and the trade is predictability for coverage of the messy cases.

Against a helpdesk macro

A macro fires on a rule you wrote and applies a template. An agent reads the thread, checks the order, decides whether the template applies, and hands off when it does not. A macro cannot decline to run.

Against a virtual assistant

The closest comparison in behaviour, and the one where the differences are most worth stating plainly: an agent works continuously rather than in shifts, has no context beyond its brief and the systems you connect, and produces a trace of every decision. A person brings judgement about things nobody wrote down, and does not need the brief to include what to do when unsure.