The 865cc parallel-twin engine is a type of internal combustion engine commonly found in motorcycles. It features two cylinders arranged side by side, which helps provide a balance of power and efficiency. The engine's displacement of 865cc indicates the total volume of the cylinders, contributing to its performance characteristics. This engine design is known for its smooth power delivery and torque, making it suitable for both city riding and highway cruising. Manufacturers like Triumph have utilized this engine in models such as the Bonneville, offering riders a blend of classic styling and modern performance.