Let’s talk about “types”

I’ve never understood the whole expression “You aren’t my type”. Why do you even have a “type”? I understand there are certain things you’re attracted to in someone, but how can you have a “type”? When people ask me my “type”, I never have an answer for them. I know what I am typically attracted to, and what I go after, but I don’t discriminate! 

Do you have a “type”, or a preference? What is it?