@McTag,
A jacket, coat, and blazer refer to the same thing. Usually, if it matches the trousers it's called a coat, as in suit coat. If it doesn't match it's called a jacket, sports jacket/coat, or blazer. If it's a particularly bright color, then it's usually called a blazer and you see a lot of used car salesmen in them.
An overcoat is much longer and usually worn when it's cold.
I don't call my trousers my "pants"
Even if they are full of ants