OOTD is an extremely popular hashtag used on Instagtam. Users use #OOTD, which stands for Outfit of the Day, when they upload photos of themselves in an outfit. Users often upload Outfit of the Day photos when they get a new outfit or feel like their outfit looks nice. The acronym OOTD is also used on social media sites like Facebook, Twitter, and Tumblr, where users share photos of outfits.