Gabrovo humour is a type of funny way of talking and thinking that people from a particular place called Gabrovo in Bulgaria use. When people in Gabrovo want to tell a joke, they often speak in a very serious way, saying something that sounds very straightforward and logical, but with a funny twist at the end. For example, they might say "Why did the chicken cross the road? To get to the other side," which is a very typical joke, but then add, "But if it had stayed home, it could have saved the energy it spent crossing the road." See how that's a little bit silly? But still kind of makes sense?
Gabrovians (people from Gabrovo) are known for being very practical and money-wise, so a lot of their jokes make fun of people who waste things or make foolish decisions. They'll often poke fun at themselves too, saying things like "I'm so cheap, I wouldn't even buy a coat hanger to hang my coat on!"
Gabrovo humour is a bit like a puzzle, because you have to listen carefully to what the person is saying and think about it before you can understand why it's funny. But it can be very entertaining once you get the hang of it!