What is Fior di Latte or Fiordilatte?

And is it cheese or a flavor of gelato?

"Fior di latte", also written as "fiordilatte", simply means "milk flower", or, less, literally, "the best part of the milk". If you're in a gelato shop, this is the simplest flavor offered. It's simply milk, cream, and sugar. Just like crema, gelato purists will often taste a new gelateria's fior di latte because it's impossible to hide behind fancy flavors or interesting preparation. If the milk isn't good, or the cream low-quality, then it's evident in the fior di latte.

I'm not sure why they missed the glass so poorly.

Sometimes, if you're on a gelato tour, the guide might say "this is basically vanilla" and that's basically wrong. As in, at its basic level, it's wrong. The evident flavor in vanilla-flavored anything is vanilla, a flavor that's clearly lacking in fior di latte. (Yes, I have so many thoughts on this.)

Wait, so fior di latte is not cheese?

You might be now wondering, if it's a flavor of gelato, why are you also seeing this on the menu at a pizzeria?

Well, fiordilatte is also a type of cheese, what many non-Italians would call "fresh mozzarella." Historically, mozzarella was made from the milk of a water buffalo, but you could also make a lower-quality version of it from cow's milk (popularized in America by Italian immigrants without access to water buffalo). To prevent people from misusing the name "mozzarella" which used to only refer to cheese from the water buffalo, they came up with "fiordilatte" which was the name to refer to cow's milk cheese. Over time, this clarity sort of disappeared, so now we still have mozzarella and fiordilatte, but, for clarification, Italians will now use "mozzarella di bufala" or "fiordilatte" to differentiate the two.

So if you're having a pizza, and you're wondering why it comes with a scoop of gelato, wonder no longer! That's just the cheese on top.