hashtag
From Longman Dictionary of Contemporary Englishhashtaghash‧tag1, hash tag /ˈhæʃtæɡ/ noun [countable] a word in a Twitter message with # in front of it, which indicates what the message is about. People can search for hashtags in order to find messages about a particular subject.hashtaghashtag2 verb [transitive] to put a hashtag before a word on Twitter