  We report on sliding Charge Density Wave (CDW) in the quasi two-dimensional
TbTe$_3$ system probed by coherent x-ray diffraction combined with {\it
in-situ} transport measurements. We show that the non-Ohmic conductivity in
TbTe$_3$ is made possible thanks to a strong distortion of the CDW. Our
diffraction experiment versus current shows first that the CDW remains
undeformed below the threshold current I$_S$ and then suddenly rotates and
reorders by motion above threshold. Contrary to quasi-one dimensional systems,
the CDW in TbTe$_3$ does not display any phase shifts below I$_S$ and tolerates
only slow spatial variations of the phase above. This is a first observation of
CDW behavior in the bulk in a quasi-two dimensional system allowing collective
transport of charges at room temperature.
