I learn something new every day! Indeed, there it is...

https://www.askdifference.com/cog-vs-sprocket/

I, too, have traditionally used "cog" or "cogwheel" to describe a geared or toothed wheel that is meshed with another geared or toothed wheel, and "sprocket" to describe a geared or toothed wheel meshed with a chain.

The English language having such wide left-and-right bounds on word meanings certainly has its benefits and drawbacks, doesn't it? Fortunately, despite that, we can usually understand each other pretty well. I heard a bike shop mechanic refer to an entire cassette as a "cog"...but I knew what he meant.