Each community in PieFed can have it's own set of "flair" options that posters can attach to their posts. Clicking on a flair will filter the community to only show posts with that flair so they function as a filtering mechanism as well as a visual identifier.
Community moderators can manage the flair that are available in their communities:
When creating posts, expand the 'more options' area to assign one or more flair to your post:
See it in action at https://piefed.social/c/piefed_meta
Flair doesn't federate yet but it will in coming days.
How will piefed's flairs federate to other fedi software? Given that piefed already has post tags, what is the difference between tags and flair?
Tags, aka hashtags, are instance-wide (not just in a community) and interoperate with Mastodon, Pixelfed, Mbin. Anyone can make a new hashtag and they are completely unmoderated.
Flairs are a limited list determined by each community's mods and are only used in that community. They will federate with other PieFed instances and with Lemmy (when they finish coding what they're calling "tags", a really unfortunate choice of name).
Ah gotcha!