What does a protruding disk with mass effect mean?

Mass effect: It means it is pushing on something, possibly a nerve or the nerve sack.

COMPRESSION: Disc protrusion implies weakness in the wall with the inner substance (nucleus pulposis) pushing outwards. The bulk or mass may be contacting a nerve root or even the spinal cord, and this statement could imply a risk to proper nerve function.

Pressing on Nerve: It means that the disk is pushing on something. Sometimes its pressing up against the spinal cord but also can be on spinal nerves.