Disc pain
A healthy disc
Disc's can give rise to pain in a number of ways. It is virtually impossible for a healthy (fat) disc to give pain but as a disc degenerates it can then become painful in variety of ways.
Annular tear

This is where as a result of a trauma (e.g. lifting) the annulus (dough) tears very much like a paper cut. This gives rise to back +/- buttock pain
.
Disc bulge

The degenerate disc is no longer as thick as it was so the outer part of the disc bulges (like squashing a doughnut). This part is called the annulus (represented here by the dough) and it is pain sensitive, therefore this bulging hurts. Also chemicals can be released from the disc that can irritate the pain sensitive structures that surround your nerves (dura).
Disc herniation/extrusion

This is where the nucleus (represented here by the jam), pushes out from the centre causing the jam to protrude. When this occurs on the side of the disc it can press on one of the nerves and can give rise to buttock/leg pain with or without weakness and pins and needles.
Disc sequestration

This is where the jam (nucleus) has been squeezed out even further and has separated from the disc. This gives rise to severe back and leg symptoms.