Is plate a countable or uncountable noun?

"Plate" can be both countable and uncountable, depending on the context.

Countable:

* When referring to individual, physical plates: "I have three plates in my cupboard."

* When referring to different types of plates: "There are many different styles of plates on display."

Uncountable:

* When referring to plate as a material: "The artist used a fine layer of gold plate on the sculpture."

* When referring to plate as a food item: "Would you like a plate of pasta?"

So, to determine whether "plate" is countable or uncountable, consider the meaning in the specific sentence.