Hashtag is among the spate of words just added to the the Oxford English Dictionary, the OED reported in a blog post today. If this news sounds familiar, it's because hashtag has already made its way into a number of dictionaries, including Merriam Webster (last month) and Oxford's own dictionary of current English (four years ago), which is distinct from the OED. The American Dialect Society made hashtag its word of the year in 2012.
Perhaps you have strong feelings about the modern usage of hashtags. They're divisive, maybe even "aesthetically damaging," argued journalist Daniel Victor in a widely shared Nieman Journalism Lab essay. They've infiltrated the way we speak in a way that, many have lamented, sounds absurd.
So hashtag's moment, clearly, has already arrived. Its graduation to the OED is significant because it signals the term's longevity; the OED shows not just what words mean but how words and their meanings have changed over time. These days, of course, "hashtag" has strong associations with Twitter and Instagram, but its roots in the language of technology—both spoken and seen—go much deeper. The OED says hashtags "originated on, and are chiefly associated with, the social networking service Twitter." (It's the "tag" part of hashtag that hints at its modern use as a cataloging tool.) But its ancestors—hash, hash key, and hash sign—have been around for more than half a century.
In that time, #—you may also know this symbol as an octothorp, number sign, or pound sign—has helped humans interact with machines in different ways. It has had its own button on the telephone since the late 1960s, and "press the pound sign" is a common prompt from automated phone systems. The symbol also has a prominent place on computer keyboards—and, before that, on typewriters—where it usually hangs out with the No. 3.
The hash symbol has been a part of how we communicate in the computer age in other ways, too. As of 1977, it was used to "indicate the presence of an octal constant in a file name or extension," according to the OED. And reporters and editors from the print era may recognize a series of three hashtags as the indicator that a story has come to an end.