There are few basic rules to follow in order to distinguish a Neapolitan pizza.
For a true Neapolitan there is no other pizza. There is only one kind of pizza.
All around Italy, there are different kinds of pizza styles, but for us Neapolitans you can call them focacce, pizze a taglio, pizze a metro, pizza romana, pizza barese, pizza “whatever.” Bottom line is, any other style needs an adjective to qualify as pizza. Neapolitan pizza is the PIZZA, no adjectives are needed.