Who? Terry Thomas was a famous British actor & comedian who became well known during the 1950s and 1960s and who had a famously large gap between his two front teeth.
In radiography, the term "Terry Thomas Sign" indicates a large gap seen on the AP view (usually ~ 4mm), between the scaphoid and lunate carpal bones indicating some kind of disruption in the scapholunate ligaments and which is often accompanied by scaphoid rotation. If not addressed, this form of CID (carpal instability dissociative) may lead to carpal collapse and significant functional impairments. Rehabilitation depends on the stage of the injury, wether the injury is acute or chronic and your surgeon's preference for operative or nonoperative management.