And they tend to be denoted by capital letters. So random variable capital X, I will define it as, is going to be equal to 1 if my fair die rolls heads. And it's going to be equal to 0 if tails. I could have defined this any way I wanted to. This is actually a fairly typical way of defining a random variable, especially for a coin flip. But I could have defined this as 100. And I could have defined this as 703.