Warrant Officer Class 2 (abbreviated WO2) is a rank in the Royal Navy, Royal Marines, and British Army. It ranks immediately below Warrant Officer Class 1, and above Chief Petty Officer in the RN, Colour Sergeant in the RM, and Staff Sergeant in the Army. It has no exact equivalent in the Royal Air Force, ranking above Flight Sergeant but below the RAF's Warrant Officer / Master Aircrew.
For more informations, see the UK section of the Warrant Officer page.
N.B.: the correct form of the rank is as given; Warrant Officer 2nd Class is incorrect, and using it within earshot of a WO2 will provoke the response "I am not a second class anything."