Niche

A niche is two decisions at once: what you make, and who it is for. Same craft, different niche, depending on whether your woodworking videos are aimed at someone with a garage full of tools or someone assembling their first flat-pack bookshelf.

The word gets used as a synonym for narrow, and narrower is not automatically stronger. A subject small enough to run out of viewers caps the channel however good the work is, while a channel covering two unrelated things gives the recommendation system nothing consistent to work with. The working test: could a regular viewer roughly predict what your next upload is about, and are there enough of those people to be worth serving?