For the similarly vague vessel designation, please see Tholian ship.
A Tholian vessel was a type of starship employed by the Tholians during the mid-24th century.
When William T. Riker participated in a battle simulation at Starfleet Academy, he calculated a sensory blind spot on a Tholian vessel and hid within it.
Many years later, in 2365, Lieutenant Commander Data noted this as one of Riker's various battle techniques while preparing for Operation Lovely Angel. (TNG: "Peak Performance")