"...Disc fissure consists of the tearing of the fibrous ring around the disc. The most usual type is radial fissure, in which the tear is perpendicular to the direction of the fibers.

Disc protrusion consists of the deformity of the fibrous ring by the impact against it of the gelatinous material from the nucleus pulposus. If the ring breaks and part of the nucleus pulposus becomes extruded, disc herniation is diagnosed.."

A better tutorial on the stages of "HNP" is here.

"...The progression to an actual HNP varies from slow to sudden onset of symptoms. There are four stages: (1) disc protrusion (2) prolapsed disc (3) disc extrusion (4) sequestered disc..."