- A single-cylinder motorcycle engine.
- A motorcycle with such an engine.
As you might guess, they go thumpa thumpa thumpa thumpa when they're running.
Torque is a vital characteristic of a motorcycle engine. While horsepower will give you top end speed, torque is what gives you pull and acceleration. Aggresively tuned multi-cylinder engines can produce plenty of horsepower, but single cylinder engines have gobs of low-RPM torque, making thumpers well suited to applications like dirt or dual sport bikes. So where race-tuned fours might lug and stall, the lowly single chugs along happy, delivering less power, but over a broader range of engine speeds. | 
