What is a rocket primarily defined as?

A rocket is primarily defined as a cylinder-shaped object that moves fast by burning gases, which fundamentally describes its operation and function. Rockets work on the principle of Newton's third law of motion, where the expulsion of gas from the combustion of propellant creates thrust in the opposite direction, allowing it to accelerate and propel itself through the atmosphere and into space. The design often resembles a cylinder for aerodynamic efficiency and stability during flight.

This definition encompasses both the mechanical structure and the essential physical principles that enable a rocket's propulsion system, differentiating it from other objects or vehicles that might share similarities in shape or purpose but do not operate on the same principles, such as balloons or aircraft wings.