The term 'BIG TRUCK' can be broken down into three separate words: RIG (3 letters), SEMI (4 letters), and VAN (3 letters). A RIG is a large, heavy-duty vehicle used to transport goods or materials over long distances. A SEMI is a type of truck that has a trailer attached to it, allowing for larger loads to be transported. Lastly, a VAN is a type of vehicle that is typically used for smaller loads, such as furniture or boxes. All three of these vehicles are considered to be big trucks, and are commonly used for commercial purposes.