Hashtag follow
Following a hashtag (not just an account) so that posts tagged with it appear in your feed. Turns the hashtag from a pure search term into a subscribable interest channel. Instagram introduced it in 2017.
Background: the hashtag (coined on Twitter in 2007 by Chris Messina) started as a way to group and search posts about a topic. Being able to follow one — e.g. #pottery or #trailrunning — turns it into a running feed of an interest, regardless of which accounts post. Win: discover new content and creators within a niche without knowing them in advance. Trade-off: spam and irrelevant posts can sneak in (people mistag for reach). Mastodon has made hashtag following central since the platform lacks a discovery algorithm — there, followed hashtags are a main way to find content. Related to sound trend and explore page.