An intimitank is a combat orientated build designed to handle mob aggro in a party. They specialize in having a high intimidate skill so they can keep the aggro of mobs from their party members. They are great to have around if you have a Rogue in your party as it helps them get many more sneak attacks and helps Rogues avoid getting the mob's attention unnecessarily.
Intimitanks usually also focus on having a high AC as having many mobs beating on them can be highly damaging, although you can find some barbarian builds who rely on their DR (damage reduction) and large hit points to work effectively in this role.
Intimitanks can be both defensive and offensive builds as it's all down to your play style.