Tactical surveillance officer (nicknamed TSO [pronounced tee-so]) was a billet common to Starfleet attack fighter squadrons, at least in the 23rd century. The TSO is the second seat weapons and targeting systems operator in attack fighters that have two or more crew.
Education for the billet usually involved two semesters' postgraduate study at Starfleet Academy in Tactical Flight Training and Support Systems Technology.
In 2274, during a mission to evacuate City Chraino, Ziboji, a Zibojian flight lieutenant and Linda Stevenson, his tactical surveillance officer, rescued a girl named Marlaina Elisabeth, last name unknown. She had no traceable relatives (or they had perished in the disaster), so the lieutenant arranged for temporary housing on the base, and for his TSO and himself to care for her. Years later, she became his legal ward. (Star Trek: Shadowstar Station)
The billet was modeled after that of radar intercept officer (RIO) on F-14 fighter planes in the 1980's. (RIO was the billet occupied by "Goose" and "Slider" in Top Gun .)