A soft landing is a landing in which an airplane or spacecraft touches down gently, without incurring damage. The opposite of a soft landing is a hard landing, in which the aircraft hits the ground hard, potentially experiencing damage or injuring passengers inside. A number of different techniques are used to achieve soft landings, with most systems being redundant so that in the event of a failure, other systems will kick in to generate a soft landing.
In order to land successfully, anything from a bird to a large aircraft needs to slow down, reduce its lift, and allow gravity to gently pull it back to Earth. Some of the ways in which this can be accomplished include stalling the aircraft, using parachutes and flaps to increase drag, and firing rockets to control descent. When the landing is accomplished properly, it should be soft, allowing the aircraft to gently lower itself to Earth.
A number of aircraft have landing gear designed for this purpose. The landing gear consists of a set of rubber wheels which are designed to grip the runway when the aircraft settles down, creating more resistance to slow the plane. Rubber is also an excellent material for a soft landing because it has some give and flexibility, allowing the aircraft to bounce as it settles to the ground, rather than jarring. Some spacecraft, such as the moon landers, use specialized feet in combination with rockets to gently lower themselves to the surface of the moon.
Soft landings are easiest when they are done on a runway, because runways are specifically designed for takeoff and landing, with the necessary space to allow an aircraft to come to a complete stop. Depending on the consistency of a ground, soft landings can also be accomplished in fields, and very skilled pilots can safely land a plane in an emergency on water, with pontoon planes being specifically designed for a soft landing on water.
Aircraft aren't the only thing which can come in for a soft landing. Hang gliders and paragliders also work to create a soft landing when they hit the ground, as do people in hot air balloons. Likewise, people who jump from aircraft with parachutes, whether recreationally or professionally, are trained to perform a soft landing to minimize the risk of injury when they hit the ground. In all cases, the soft landing reduces the risk of injury, and ensures that no damage occurs, so that the aircraft or device used for flight can be used again.