A spin-stabilized satellite is a satellite

Satellite

In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

 which has the motion of one axis held (relatively) fixed by spinning the satellite around that axis, using the gyroscopic effect.

The attitude of a satellite or any rigid body

Rigid body

In physics, a rigid body is an idealization of a solid body of finite size in which deformation is neglected. In other words, the distance between any two given points of a rigid body remains constant in time regardless of external forces exerted on it...

 is its orientation in space. If such a body initially has a fixed orientation relative to inertial space

Inertial space

In physics, the expression inertial space refers to the background reference that is provided by the phenomenon of inertia.Inertia is opposition to change of velocity, that is: change of velocity with respect to the background, the background that all physical objects are embedded in....

, it will start to rotate, because it will always be subject to small torque

Torque

Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

s. The easiest form of attitude stabilization is to give the rigid body an initial spin around an axis of minimum or maximum moment of inertia. The body will then have a stable rotation in inertial space.