Spithead, strait of the English Channel, forming an extensive, deep, and sheltered channel between the northeastern shore of the Isle of Wight and the mainland of England. The Spit Sand forms the western side of the channel leading into Portsmouth harbour. Besides its special association with the Royal Navy—major naval reviews have been held off Cowes (on the Isle of Wight)—Spithead provides the safest approach for large craft entering and leaving Southampton Water, one of England’s most important commercial harbours. A lesser channel, The Solent (q.v.), forms a westward continuation of the Spithead strait.