How many outcomes are there in the sample space for tossing 2 coins?

Ultimately, one can define one's events and sample space however one wants. But we usually design it with some sort of problem in mind. You can understand it by assuming that 1 coin is red and the other is black. In this case there are exactly 4 outcomes when you flip these 2 coins, that is HH, HT, TH or TT.