noun 1.(on social-networking Web sites) 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. 2.a hash mark used in this way.
verb (used with object), verb (used without object), hash·tagged, hash·tag·ging. 3.to add a hashtag to (a word, topic, or message): Someone on Twitter just hashtagged the film festival.
