Alonzo, the primary bevel of a blade is the main grind from back to edge. It can be full or partial, that is, starting partway down from the back. It can be convex (bowed outward) or flat or concave, generally known as hollow (bowed inward). It can be chisel ground, sharpened only on one side, the other left untouched.
All of these can be ground right down to the edge, so both sides meet in a very sharp line. But this will be somewhat delicate, and the edge can roll or chip fairly easily. So most blades are given a secondary bevel, and the user forgets about the primary grind and focuses on this edge bevel, whether it is acute or obtuse, and especially whether it is wide or narrow.
A narrow secondary bevel is hardly there. It takes some of the sharpness of that delicate edge off and substitutes toughness instead. But if the secondary bevel is very narrow, it won't interfere much with the edge slicing into material, especially if the edge of the primary bevel behind it is relatively narrow.
