  Eigenvectors of stress-energy tensor (the source in Einstein's equations)
form privileged bases in description of the corresponding space-times. When one
or more of these vector fields are rotating (the property well determined in
differential geometry), one says that the space-time executes this rotation.
Though the rotation in its proper sense is understood as that of a timelike
congruence (vector field), the rotation of a spacelike congruence is not a less
objective property if it corresponds to a canonical proper basis built of the
just mentioned eigenvectors. In this last case, we propose to speak on
pseudo-rotation. Both properties of metric, its material sources, and
space-time symmetries are considered in this paper.
