"christmas break"

Somebody told me that it's "politically incorrect" to call winter break christmas break. Why? What does politically incorrect means? The first thing that comes to my mind when I hear this term is that it does with politics lol

I'd assume that's because christmas is a christian holiday, not everyone celebrates christmas so I guess some people might feel offended if you call it "christmas break". If you call for example overweight people "fat" or black people "niggers" or small people "midgets" you are being polically incorrect. So basically it means that you use a possibly offending term instead of the most neutral one.