Ogre lords are special ogres that lead other ogres. They appeared in Warcraft III as large two-headed ogres or as ogres in unique armor. They appear in The Burning Crusade with a new model, a one-headed ogre with growths coming out of its back and head.
It is both a rank among ogres, and a race of ogres. Though the race may hold the rank, they are not the same.
Azeroth ogre lords
Many of the ogre lords have rallied the remnants of their people that were scattered when the horde fell. Though their plans are unknown, there is no doubt that these powerful, deceptively intelligent warriors will gather their forces once more. Using their immense bulk to terrorize their lesser ilk into service, ogre lords are often encountered guarding Gold Mines, Healing Pools, and other valuable locations. Although they do not cast spells, ogre lords make up for their lack of magic with pure brawn, blasting their tree-trunk sized clubs into their enemies' skulls with unequaled fury. The ogre lords of Stormwind emerge to stake claims on the wild lands, resulting in rising clashes between all races in the region.
Outland ogre lords
From the archive page World of Warcraft: The Burning Crusade - Bestiary:
It is believed that the massive, cyclopean Gronn are the ancient ancestors of the ogres. If so, the ogre lords of Outland are the only ogres known to retain some of the physical traits of their gronn progenitors, such as the bony, calcified protrusions on their head and back, as well as a portion of the gronn's immense size and strength. Other unique characteristics possessed by the ogre lords are their intelligence and reasoning abilities, which are more acute than those of their ogre cousins. This combination of brute strength and increased intellect make the ogre lords worthy of both respect... and fear.
Like the gronn (and unlike most ogres), the ogre lords have only one eye and have stone-like growths covering their bodies. It is possible that heads of the ogre lords (or their unknown, immediate descendants) were used in the process of creation of two-headed ogres (since the second head looks very similar to that of an ogre lord). More likely, ogre lords are simply more closely related to gronn than regular ogres.
Many two-headed ogre lords could be seen in Warcraft III leading bands of ogres.
Known ogre lords