虽然物理学理论上没有绝对静止的物体和体系，但为了研究某些问题的方便我们常常会假定某一物体或体系静止，用其他物体相对于该体系所表现出的运动学参数（如相对速度、相对位移）来描述该物体的运动状态，选定的这个假定静止物体或体系就称为静止参考系。因为静止参考系选取的差异会引起对同一物体运动状态描述的不同，所以最好能在描述运动时指明所选的参考系。解决一般机械运动时常选取地面做静止参考系。静止参考系也简称为参考系、参照系。

In special relativity the rest frame of a particle is the coordinate system (frame of reference) in which the particle is at rest.

The rest frame of compound objects (such as a fluid, or a solid made of many vibrating atoms) is taken to be the frame of reference in which the average momentum of the particles which make up the substance is zero (the particles may individually have momentum, but collectively have no net momentum). The rest frame of a container of gas, for example, would be the rest frame of the container itself, in which the gas molecules are not at rest, but are no more likely to be traveling in one direction as another. The rest frame of a river would be the frame of an unpowered boat, in which the mean velocity of the water is zero. This frame is also called the center-of-mass frame, or center-of-momentum frame.