"Nvm" is an abbreviation that stands for "never mind". It is used in informal communication, especially in messaging apps, chat rooms, or texts when someone wants everyone else in the conversation to disregard their last message. It can also be used to ask someone to disregard the previous message you have sent, or to explain that you do not need help anymore. "Nvm" can be written in both upper- or lowercase, but the latter is much more common.