A person who is overly nice (only to girls) for no reason. A simp is NOT a gentleman. The only simping that is ok is if you once in a while simp to your girl because you want something from her and/or want to hook up.
Holly (girl) is looking for a seat at a dinner party...
Hey Holly, do you want to take my seat? (Adam says)
Adam, you are a major Simp. You probably have 3 total friends.
You deserve a chair to the face.