Algorithm, Search & Distribution
Hashtags
Also called: hashtag
Put a hashtag in a description and it becomes a link to a page collecting everything else tagged the same way. YouTube pulls up to three of the ones it judges most engaging and displays them above the video title, which makes the first few worth choosing on purpose. Go past 60 on one video or playlist and every hashtag on it gets ignored.
On Shorts they no longer do much for discovery, though one to three relevant ones cause no harm and give a viewer some context before they commit. Creators load a description with tags as though volume helps. Past the handful shown by the title, the rest sit there as links somebody can follow.