The official entry reads as such: "Twerk, v.: dance to popular music in a sexually provocative manner involving thrusting hip movements and a low, squatting stance."
Twerking has been around for almost 20 years, first appearing in hip-hop in New Orleans. It was later popularized in the early 2000s thanks to the Ying-Yang Twins, with songs like "Whistle While You Twurk."
Katherine C. Martin, head of US Dictionaries at Oxford University Press, said in a tweet that the addition was not reactionary to Miley Cyrus' now-infamous twerking at the VMAs over the weekend. She posted, "Planned months ago, I swear!"
The Oxford Dictionaries Online is a bit more progressive with the addition of words and its collection is separate from the official Oxford English Dictionary, although they are owned by the same group. Words added by the ODO can fade to obscurity rather quickly, due to the nature of Internet slang. The OED waits several years to establish continued use before adding words.
Other words added by the ODO include TL;DR (Too Long; Didn't Read), derp (used as a substitute for speech regarded as meaningless or stupid, or to comment on a foolish or stupid action), srsly (slang short for seriously), unlike (for its use in disliking social statuses), jorts (slang for jean shorts), and selfie (slang for taking a photo of yourself).