The American English term is called "Lump Head". It can have more than two meanings.
The translation is somewhere between Klumpenkopf and Dorftrottel. 😀

If you want to know more, Jerry is the man. Not that his head is or isn't lumpy after that motorcycle accident. 😀

It's about removing head port obstructions, inserting an air-foil "lump" and increasing the valve diameter to improve the flow to the engine.

Here are some dyno runs on a 292 with a stock cam.
https://www.12bolt.com/65279inline-cylinder-head-flow65279.html

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."