The term 'Convoy Truck' refers to a truck that is part of a convoy, which is a group of vehicles traveling together for safety and protection. The two crossword solutions for this term are 'RIG' (3 letters) and 'SEMI' (4 letters). 'RIG' is a slang term for a large truck, usually used to transport goods over long distances. 'SEMI' is short for SEMI-trailer truck, which is a type of truck that has a trailer attached to the back. Both of these terms refer to large trucks that are commonly used in convoys.