Well, I personally never use the word "dating" but my boyfriend does, and to him it means pretty much the same thing as going out - he refers to us as "dating." For other people, I think it means something a lot more casual though. Seeing each other is slightly less commitment, I think - you haven't yet decided if you want a relationship, and it might not necessarily be entirely exclusive. But really these things can't be defined in a way that everyone will agree with.