The ROFL-Dance is a dance, in which (usually) a stickman dances. The song itself is Jun. A's version of Greenwich in the Sky. It also includes flashing lights/patterns, and thus is not recommended for epileptics to watch.
Many of the people just call it the ROFL-Dance Song, as they're unaware of the song's origins.
It may also include words LOL, ROFL, OMG and so on for the sake of it being the "ROFL-dance".
ROFL Dance is a simple dance.