Dance Quarterly is a magazine which Squidward has a subscription to. As it says from its title, the magazine is obviously about dancing.
It is first seen and mentioned in Can You Spare a Dime?, when Mr. Krabs asks Squidward "Hmmm, are you prepared to say that with your hand on top of a stack of interpretive Dance Quarterlies?" It is also seen in the episode The Camping Episode, where Squidward looks at his Dance Quarterly Magazine calendar in his bedroom about the day SpongeBob and Patrick go camping.
Dance Quarterlies have a light blue cover which reads "Dance" in capitalized red letters and "Quarterly" in lowercase white letters.