- (on social media websites) a word or phrase preceded by a hash mark (#), used within a message to identify a keyword or topic of interest and facilitate a search for it: The hashtag #sandiegofire was used to help coordinate an emergency response to the fire.
- a hash mark used in this way.
verb (used with or without object), hash·tagged, hash·tag·ging.
- to add a hashtag to (a word, topic, or message): Someone on Twitter just hashtagged the film festival.
- (on the Twitter website) a word or phrase preceded by a hash mark, used to denote the topic of a post