What is inseam length?

On pants, what is inseam length? Is it the second dimension in the size? For example, I'm a 28x30 (I'm 14 and my legs are hella long) so is 30 the inseam length there? Because I know 28 is the waist measurement. I need to know because I'm buying a pair of pants online and will not be able to return them if I don't like them. Thanks, best answer gets ten points.