Nuchal Hump

From The Aquarium Wiki

The Nuchal Hump is visable on male fish, mainly on Cichlids, as a hump on the forehead, depending on species, it can be fairly subtle, or extremely prominant. It can also be referred to as a Kok.

They can be highly prized in show fish, especially on the Flowerhorn hybrid cichlid, the larger the Nuchal Hump, the more expensive it will be to buy.