Now the Oxford Dictionaries have the new entry "Twerk, verb," to answer that question.
Srsly. (Which, also added to the dictionary, means "seriously.")
The definition: ‘‘Twerk, v.: dance to popular music in a sexually provocative manner involving thrusting hip movements and a low, squatting stance.’’
It sounds like Oxford got the definition of what Cyrus did on stage to fellow performer Robin Thicke just about right.
There are many theories about the word, which some speculate is a cross between twist or twitch and work, in the context of "work it," a phrase frequently used to encourage dancing.
Lousiana's DJ Jubilee used the word as early as 1993 on "Do the Jubilee All." Then there was some back and forth on spelling the word. Atlanta's Ying Yang Twins put out “Whistle While You Twurk” in 2000 and Usher released “Twork It Out" in 2001.
More recently, twerk has become the accepted spelling with this summer's “The Twerk Song," by Cash Out and “Twerk It" by Nicki Minaj and Busta Rhymes.
Other pop culture-fueled terms to make it into the dictionary include 'selfie', emoji', and 'Bitcoin'. The word 'fomo' was added, originally an acronym for "fear of missing out." Another word that may be real in print but is probably rarely spoken is 'phablet', a phone-tablet hybrid.