It refers to the popular musical style called "Rock 'n' Roll," or "rock" for short. It is not the same as the song "Jingle Bells." "Jingle Bells," written in the 1800s is one of the best-known U.S. songs in the world. It has the refrain: Jingle bells, jingle bells, jingle all the way. Oh! what fun it is to ride In a one-horse open sleigh! "Jingle Bell Rock" begins: Jingle bell, jingle bell, jingle bell rock Jingle bells swing and jingle bells ring... Sometimes old songs are re-scored in a new style, by changing the rhythm or instrumentation. The title "Jingle Bell Rock" suggests a rock 'n' roll version of "Jingle Bells." It isn't. It isn't really in the rock 'n' roll style, either. It was published in 1957, which is about the time that rock 'n' roll really started to become widely known in the United States. They just called it "Jingle Bell Rock" to suggest something new and up-to-date. "Jingle Bell Rock" is a fairly popular Christmastime song like dozens of others. Most people in the U.S. know it and can hum the tune. It is not a deeply beloved favorite, though. It is not the sort of thing a family or a group of friends would sing together; not everyone would know enough of the words. "Rock 'n' roll" is a popular musical style. Its roots are African-American and date from the 1920s and 1930s. It exploded into popularity in the United States in the 1950s, when popularized by radio disk jockeys, particularly when it began to be performed by white singers like Elvis Presley.

As in 'rock and roll' :)