Can someone please tell me what does partial sacralization of the lateral aspects of l5 mean ?

Born with it: So basically, L5 is the last of your lumbar (low back) vertebrae and it sits on top of the sacrum which is the end of your spine. The transverse processes, or "arms" if you will, of the L5 sometimes are fused to the sacrum as an abnormality that you are born with. It can cause low back pain, or it can by asymptomatic. If it's partial, then there is only slight and not complete fusion.

Anatomic variation: It is an anatomic variation whereby L5 is partially incorporated into the sacrum, rather than being completely separate. It is usually an incidental finding of no concern, but occasionally the transitional articulation between L5 and S1 can develop degenerative changes.