Art Rock is a sub-genre of Rock-and-roll music that originated with the hippy culture of the late 1960s and reached its peak in the 1970s with bands like Genesis, Pink Floyd, and Yes. Art Rock generally incorporates other forms of music such as jazz, and seeks to create a mood (which is better for listening than for dancing).
The term originated in reference to bands such as pink floyd, who's members originally went to art school, but now can apply to even bands such as Thursday and Mineral.
Often confused with progressive-punk. Indeed, they were once synonyms, but over time have diverged; prog becoming it's own genre of music while art rock maintaining loose and subjective to interpretation.