As you may know, I am in Italy and learning about Mediterranean cuisine as an accredited nursing course. Our instructor, June, said that pizza used to be known as the poor man's bread. Centuries ago bakers would throw in a mixture of flour and water into the ovens to test the temperature of the oven. Based on how this floury paste turned out would be when they knew the oven was ready for their real bread.
The bakers would take out this flat bread from the ovens and then give this "waste" to the poor. The poor would take the flat bread and dress it up with olive oil, tomatoes, and seasoning. In the 1800's this poor man's flat bread began to be sold by street vendors. It was then called pizza.