Double hump heads

I'll be the first to admit that I know nothing about Chevrolet stuff. I know the common engine sizes and such but I have no clue on how to tell them apart. But ever since I was a kid I have always heard the term double hump heads for Chevrolet stuff you know them 300hp double hump heads on a tree fitty. But never knew what they was or how to tell them apart I always thought it had something to do with the port design or something. I just learned that its a casting mark on the end of the head. Seriously chevy? Why?? Now im gonna double roll my eyes everytime I hear someone say double hump heads. Why not just give them a number or something. Am I the only one that finds this ridiculously stupid? Lol