To lip sync is to move the lips in time with a recording instead of singing live, a technique familiar from music videos, television studios and tightly choreographed shows where dancing and breathing compete for the same lungs. Merriam-Webster dates the verb to around 1961.
What used to be a slightly awkward secret has become a celebrated sport. The idea of a lip-sync contest between celebrities came from the actors Stephen Merchant and John Krasinski, who dreamt it up while brainstorming with Emily Blunt before Krasinski appeared on Jimmy Fallon’s Late Night. Fallon made it a recurring segment, and on 2 April 2015 it became a series of its own, Lip Sync Battle on Spike, hosted by LL Cool J with Chrissy Teigen as commentator. Stars now win applause by miming other people’s hits with total conviction, which may be the most honest form of fandom there is.