Featured notes are the ones visible on your "homepage". There's a setting that allows you to determine which notes are featured by hashtag. So you could define a hashtag called #featured and only notes with that hashtag would appear on your homepage. And you can define as many different hashtags as you want. There's also a general inclusion setting that defines which hashtags are included at all in your website.
Yeah I tested them all and found one I liked. Can't seem to figure out what determines a *featured* note or how to select/deselect features notes - but still pretty cool for free! Updated my URL to https://bfgreen.npub.pro/
Discussion
Sorry for the confusion. Featured (pinned) posts are supported by some themes. You set Pinned posts in site admin panel, and those posts will always show at the top, and in supporting themes will be marked as 'featured'. Homepage hashtags are useful too, but those only filter posts, they don't prioritize them or mark them as featured.