Pop is short for "popular", so pop music is basically what's popular at the time you're listening. But it also means songs that are easy to listen to, because they follow simple chord progressions, simple arrangements, and a simple song format.

The most common format in pop music is introduction, verse, pre-chorus, chorus, verse, pre-chorus, chorus, bridge, and chorus. So it's pretty repetitive.

[ Listening to a pop song might make it easier to understand, though. ]

Am I making sense?