Telmor was a hidden draenei-populated city that was once located in Talador on Draenor, now Outland's Terokkar Forest. It was built on a mountainside and was the closest draenei settlement to Auchindoun. The city was located in the middle of ogre country and made invisible by a protective spell using Leafshadow, a shard of the Ata'mal crystal.
Rise of the Horde
When and his draenei party had rescued the young orcs and Orgrim who were under attack by an ogre, they were escorted to Telmor and Durotan memorized the incantation that deactivated the spell. Later, when the orcs started a war against the draenei, Durotan used this knowledge to remove the invisibility spell from Telmor, leaving the nearly undefended city open to attack. As a result, the city was taken over and completely destroyed, and Restalaan was killed.
After this, the city was offered to Durotan and his clan but he refused, so and his Blackrock orcs gained control of the city.
Given Telmor's position south of Auchindoun, it was presumably lost when Draenor was destroyed and became Outland.