Whats an obsidian tank?

I have heard in many threads about obsidian tanks, but i dont know what they are.
Any help?

http://www.pvxwiki.com/wiki/Build:W/E_Obsidian_Tank

I never tank because tanks suck and are not needed, so I don't know if it's a good build or not.

Quote: he Obsidian Tank takes the high armor/health/durability of the warrior class, and adds to it the defensive capabilities of the Elementalist Earth Magic enchantments. It's purpose is to take/hold aggro and soak up damage. It is strictly a PvE build with little use outside of very high level areas like the Domain of Anguish and Sorrow's Furnace, where variations of this build have been a staple for ages. It pairs very well with a monk bonder build. Quote from http://www.pvxwiki.com/wiki/Build:W/E_Obsidian_Tank

Check the link for the usage/skills etc.