If you visit the Balkans make sure to try it. There are many variations of the börek and all them are great.
In Bosnia, "börek" (or "burek", as is its local spelling) is only filled with meat, while the rest of the dishes fall under the broader category of "pitas" (or pies): sirnica (filled with cheese), krompiruša (filled with potatoes), zeljanica (filled with cabbage), jabukovača (filled with apples)...
In Serbia and Croatia, they're all "burek" with different stuffings, so burek with cheese, burek with potatoes, etc.
It's a weird hill to die on, but you will receive some weird looks if you request just "burek" in Serbia/Croatia/Montenegro, or "burek with cheese" within Bosnia.
Most typically 'me mish' or 'me spinaq' - with meat or with spinach.