A plasma shock was a physical experience caused by contact with plasma that was very painful but which did not cause any lasting physical harm. It was also strong enough to overload the neural net of a Soong-type android like Data.
Lieutenant Commander Geordi La Forge and Ensign Ro Laren tried to plasma-shock Deanna Troi, Data and Miles O'Brien in 2368 when they were taken over by Ux-Mal criminals. The shock was powerful enough to send Troi and O'Brien to the ground and made the criminals temporarily leave their bodies. (TNG: "Power Play")