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