my favorite food is pizza
Mmm. I love pizza. I am from the NY metro area and am a pizza snob. lol The word pizza was first documented in AD 997. Didn't realize it was that old. 
was it originally from Italy?
No, it wasn't. The precursor of pizza was more then likely the focaccia. It was a flat break known to the Romans as "panis focacius.". Toppings were then added to it. 
so what makes a pizza a pizza :)
It was in the late 18th century when tomato was added to the focaccia in Naples.