Eighteen-wheelers are large trucks that are used to transport goods across long distances. They are also known as SEMIS (5 letters) or rigs (4 letters). These vehicles have eighteen wheels and are usually driven by professional truck drivers. They are often used to transport large loads of cargo, such as construction materials, agricultural products, and manufactured goods. Eighteen-wheelers are an important part of the transportation industry, helping to keep the economy running smoothly.