Orbital velocity refers to the minimum velocity required for a planet or any object to maintain a stable orbit around a central body, such as the Sun in the case of planets within our solar system. It represents the speed at which the gravitational pull of the central body and the forward motion of the orbiting object balance each other, resulting in a circular or elliptical orbit.

The orbital velocity of a planet is determined by two main factors: the mass of the central body and the distance between the planet and the central body. According to Newton's law of universal gravitation, the gravitational force between two objects is directly proportional to their masses and inversely proportional to the square of the distance between them.

For a planet in a stable orbit, its orbital velocity must be high enough to counteract the gravitational pull of the central body. If the object's velocity is too low, it will be pulled toward the central body and crash into it. If the velocity is too high, it will escape the gravitational pull and move away from the central body.

The orbital velocity of a planet decreases with increasing distance from the central body. This means that planets farther from the Sun have lower orbital velocities compared to those closer to the Sun. For example, Mercury, being the closest planet to the Sun, has a higher orbital velocity than Earth. Similarly, Earth has a higher orbital velocity than Mars.