I've chosen to define "agency" as pretty much "the thing that humans can do and agents can't". To me, agency is the thing where you independently decide what it is you want to get done in the world, based on your own inherent goals.

Being able to say "the one thing agents don't have is agency" is a really useful way to help people understand why people still matter.

Setting software agents loose on the world to make their own top-level decisions about what they're going to do is a great way to infuriate Rob Pike https://simonwillison.net/2025/Dec/26/slop-acts-of-kindness/ or unfairly attack the reputation of Scott Shambaugh https://theshamblog.com/an-ai-agent-published-a-hit-piece-on... or waste the time of your local police permit office and suppliers https://andonlabs.com/blog/ai-cafe-stockholm