hashtag

Etymology

From earlier hash tag, from hash (sign) + tag. The hash sign # was initially proposed as tag hash by Chris Messina to create groups on Twitter, modeled after the IRC channel prefix. First published use as hash tag by Stowe Boyd in 2007.

noun

1. (Internet) A metadata tag, signaled by a preceding hash sign (#), used to label content.
   I support the hash tag convention: http://tinyurl.com/2qttlb #hashtag #factoryjoe #twitter 2007 Aug 25, Stowe Boyd, tweet, https://twitter.com/stoweboyd/status/226570552
   You can also search for a hashtag by typing a topic (without the #) in the search box and clicking Search. 2009, Paul McFedries, Pete Cashmore, Twitter Tips, Tricks, and Tweets
   While hashtags aren't formally part of Twitter, some clients, such as Tweetdeck, will persist hashtags across replies to create a sort of message threading. 2009, Alistair Croll, Sean Power, Complete Web Monitoring
   The planes are moving into position. The foreign ministers of minor Arab states are taking calls on their cell-phones from Western politicians. Twitter accounts explode around the Libyan hash-tag. 2011, Rory Stewart, “Here we go again”, in London Review of Books, 33.VII
2. (Internet, informal) The hash sign itself, when used as part of a hashtag.
   I sound like a shitty mother and wife. Or at the very least an inadequate wife and ungrateful mother–which is in stark contrast to the image I try to portray on Instagram. Hashtag happy life. Hashtag beautiful family. Hashtag blessed. 2016, Emily Giffin, First Comes Love: A Novel, New York City: Ballantine Books, page 40
   You're perpetually stoned, aren't you? Hashtag four twenty four seven. 2018, John Allison, By Night, volume 1, Los Angeles, CA: Boom! Box, page n.p.

verb

1. (transitive, Internet) To label (a message) with a hashtag.