Steven Universe - It's Her!

Emeralds and Nephrites seem to have similar roles, but at the same time there are notable differences. The Emerald commands a space warship while the Nephrite commands a troop dropship. Thus the Emerald is more of a Naval officer, while the Nephrite is more of a Marine commander.

Probably just a name to make it sound cool, like how Star Destroyers in Star Wars can't actually destroy stars