The Full form of OOTD is Outfit of the Day. OOTD is a popular internet slang which is widely used in fashion blogs, social media sites like Instagram, Facebook, Twitter, Tumblr, Reddit, and even on videos uploaded on YouTube. For example, hashtag OOTD (#OOTD) is used when someone uploads their pictures in a dress or feel like the outfit they are wearing is looking nice or want to show the clothes they wear on a specific occasion or day. It is believed to be a variant of WIWT (What I Wore Today), and is used to indicate what a person has worn to others. Photos that are generally taken in a full-length mirror are used to express OOTD.