What is the difference between "a priori knowledge" and "a posteriori knowledge"?

Put shortly, whether something can be know "a priori" or "a posteriori" depends upon whether it can be known from experience or without experience. A priori knowledge is knowledge that can be known independent from any experience. For example, "All crows are birds". Mathematical equations are also examples of a priori knowledge, since we do not need to experience something in the world to know that they are true. A posteriori knowledge, on the other hand, is any knowledge that does require experience as justification. For example, "It's sunny outside", or "Lily has red hair". Whereas a priori statements can be known in an of themselves, a posteriori statements must be verified by some empirical experience.