They tend to be just triads whereas in classical music we can have a triad but we can also add a seventh note with one,three,five,seven,nine,eleven, that kind of thing.

流行乐一般只用三和弦，但是古典乐可以用三和弦,也可以在上面加上七音，一，三，五，七，九，十一，诸如此类的。

耶鲁公开课 - 聆听音乐课程节选