…Hashtags are curious words and mashed-together phrases earmarked with a hash symbol (better known, perhaps, as the pound sign). When a hashtag is included in a Twitter post, it signals which topic the tweet is believed to address. It’s shorthand that works sort of like the moment in a conversation when a big talker might say — generously to a newcomer, pointedly to a dummy — “We’re talking about the future of the Democratic Party here.” A hashtag (think #futureofthedemocraticparty) is also a link, so anyone who encounters one on Twitter can instantly search the network for that phrase. (This week’s On Language, on Page 12, has more on the etymology.)
Where library science uses shared, intuitive and (in principle) value-neutral systems for organizing information, Twitter users often classify their tweets in the most condensed, most charged and least transparent way possible. While aiming to draw people in, Twitter users nonetheless strive for unique hashtags (#freeskip instead of #gates, for example) so that searches don’t retrieve off-topic stuff. I can say this from experience: If you urgently want to know about the Gates arrest, you want to dodge tweets about Bill Gates’s quitting Facebook. That nonnews is for #billgates people.