OTG on TikTok stands for out of the group. This is a hashtag that is used to indicate that a user is no longer part of a specific group or clique. It can be used to show that someone has left a particular social circle, or it can be used to indicate that someone is no longer interested in participating in certain activities. OTG can also be used as an insult, to suggest that someone is not cool enough to be included in a group.