What does Pennsylvania-class ship mean?

Answer 1

Naval ships are grouped by "class" this is different from "type".

Basically a class is a group of ships built from the same plan.

A ship class is traditionally named after the first ship of that Class.

Pennsylvania Class ships were a class of Battleships, basically an improvement of the slightly older Nevada Class, the first of which was the USS Pennsylvania followed by the USS Arizona.

The US navy built a series of small two/three ship classes during and after WW1 each class being a slight improvement of the last - resulting in 12 ships in total which were close enough in design to work as a group despite being 5 different classes, these ships were the main US battle fleet between the wars and the 8 of them in the Pacific were the target of the Japanese attacks on Pearl Harbour.

USS Arizona was sunk there, USS Pennsylvania survived and after repairs went on to serve throughout WW2 but after taking a torpedo near the end she was used as a target in atomic bomb tests.