Those that use cliche dance moves like "the sprinkler" because they can not dance and it is all they know. Usually their "moves" do not fit with the song.
Ross is definitely dance challenged, he got out on the floor and started doing disco moves to the song Sweet Caroline.
Those that have little or no natural ability to dance. The same group often does not let this lack of ability deter them from dancing.
Catherine is dance challenged, when she dances she only uses her shoulders, and often raises her hands wildly.