Displacement is a vector quantity that specifies the change of position of a body or particle and is usually measured from the mean position or position of rest. In general, it can be represented as a rotating vector or a translation vector, or both. Displacements can either be absolute (i.e. relative to fixed axes) or relative (e.g. a shaft relative to a bearing). Sinusoidal displacements can be measured in peak, peak to peak, or r.m.s. terms.