Gangland is the world of organised, violent crime — the bosses, the shootings, the hidden rules. Newspapers use it most often in front of another noun: a gangland killing, a gangland boss, a gangland war. That “killing” sense in the gloss is the typical story, but the word itself is the scene those stories happen in, not the murder alone. It is crime-report and film language, a little dramatic on purpose. Land here is not a country you can point to on a map; it is “the world of”, the same trick as in filmland. So gangland is “gang country” in the social sense: where gangs hold power. You can say it in both British and American English. It is darker and more serious than playground talk about a “gang” of friends.