An Ore Slime is a type of slime that spawns underground. When killed, it drops a random amount of the ore it is named for.
There are a total of 19 different Ore Slimes, one for each prehardmode normal ore tier and 1 for each of the hardmode starter metals. In prehardmode, only the Ore Slime that corresponds to the ore you have in the world will spawn, but in hardmode, any hardmode ore slime will spawn. List of the slime types:
Copper, Tin, Iron, Lead, Silver, Tungsten, Gold, Platinum, Rhodium, Osmium, Cobalt, Palladium, Duratanium, Mythril, Orichalcum, Naquadah, Adamantite, Titanium, and Troxinium.