What is the difference between a Mexican tortilla and a spanish tortilla?

A Mexican tortilla is either made from mainly flour or corn and is a flat type of bread (pan).

A spanish tortilla (Spain) is similar to the American omelette. There are several types of Spanish tortillas depending on what is placed in them, or there is a tortilla de patatas which is like a potato cake made from eggs and potatoes that is seasoned with usually either bacon, vegetables, onion or tuna.