And it's a pretty, hopefully you'll find, straightforward idea. If you're doing a trial, something that is probabilistic, a trial or an experiment, a sample space is just all of the, it's a set of the possible outcomes. So a very simple trial might be a coin flip. So if you're talking about a coin flip, well then the sample space is going to be the set of all the possible outcomes. So you could get a heads, or you could get a tails. That right over here is the sample space for the coin flip. So, and it's very useful because, for example, if these are equally likely outcomes, and you say, well what's the probability of the event of a heads?