what meant stationary and rotating polarcovalent molecule ?

@ mardana 
the covalent molecules which have dipole moment as 0 are called as stationary polar covalent molecules . 
there are also no degree of freedom of these molecules . 
rotating polar molecules are those moleculkes which are not stationary but rotating about its axis , thus , this molecule exhibits rotatary motion about a perticular axis . 
hope it helps 
all the best ..