A targ pit was an area aboard a Klingon starship where targs were kept.
In 2154, Doctor Arik Soong threatened the Augment Malik that he would be locked in their stolen Klingon Bird-of-Prey's targ pit and wouldn't "see the light of day for a month" if he continued to disobey the doctor's instructions. (ENT: "The Augments")
The area where T'Pol and Hoshi Sato discover targs aboard the IKS Somraw in ENT: "Sleeping Dogs" may have been a targ pit.