It feels like every other day there's a new TikTok trend taking over the app. One new phrase for many users is "IYKYK," and so many of us have constantly caught ourselves trying to understand what a particular string of letters means. So, what does it actually mean?What does 'IYKYK' mean on TikTok?On TikTok, and social media in general, IYKYK means "If you know, you know." A lot of creators use this hashtag or in a post's caption when talking about things that may pertain to a certain group of people who will relate to their content. If you're considering using it and aren't sure how, it's most likely properly placed when someone has to have had firsthand experience with something to truly understand.\n\nThe phrase is also often used to signal to people with shared interests or fandoms. For example, one TikTok user created an outfit video featuring a specific sweater, captioning the post with "#IYKYK" — fans of Harry Styles would recognize that the sweater is a popular one that he wore in the past.TikTok user Sydnee Mykel has an example of this in her video where she's laying on a bed staring up at the ceiling and shaking her head. "Do y'all ever just ...," Sydee put in the post's caption while a mashup of "Feels" by Kehlani, "Girls Need Love" by Summer Walker, "Focus" by H.E.R., and more played over it. Featuring the hashtag "IYKYK," many people were in the comments talking about how they can relate to the feelings this TikTok portrays."Look at the ceiling and think myself into sadness," said one comment, "Yep! Every single day." Other comments talk about breaking up with someone and resisting the urge to reach out to them. "There are so many scenarios I could use to describe this feeling," said another comment. "It’s part of my daily routine now."But these kinds of videos aren't always about such serious topics. In June 2021, Tana Mongeau posted a TikTok with Gage Gomez. The caption said "IYKYK," and fans understood they were throwing shade at James Charles. Tana and James used to be friends, although it's not clear why they stopped talking. In the past, James said that Gage used him for free Coachella tickets.Did 'IYKYK' start on TikTok?Although it's not completely clear where IYKYK started, it's definitely a social media staple. This is most likely because the internet is full of content trying to be relatable, and because people love to show others that they're part of an exclusive group. Relating to a post that says "IYKYK" can make you feel like you're in on a secret, or it can show you that you're not alone in how you're feeling — whether it be negative or positive.In various comment sections where IYKYK is used, creators are talking about how other users are reaching out to them, feeling relieved that others can share in their experience. It's creating a sense of community for those who have faced similar struggles or more lighthearted experiences.