The Fender neck profile system. It's the same designation for basses as it is for guitars. C shape, U shape, and V shape. There are different variations of each shape. You could have a hard V. It's literally the cross section of the neck follows the shape of a letter. I have two examples here. I have an example of a U shape and an example of a C shape. This is from 79 P-Bass. This would be a C-shaped neck, a pretty soft C. If you have a hard V it really just points straight out like a V shape. If it's a soft V it's out a little more but rounded at the tip. A U-shape is like a big baseball bat style neck which I'll show you in a second. This one is the C.
A lot of the reissues that they do, they go for the V. It's sort of a classic like 50s vibe. That's where it's most commonly seen. A lot of the reissue guitars that Fender does are based on models of 50s guitars that those artists played, like the Clapton signature model. He played a 50s Stratocaster, so his custom shop Eric Clapton model Strat has a hard V-shape neck on it. An example of a U-shape neck would be on this Telecaster bass behind it. I'll show you. You can see how much more depth there is to it than the C, and how abrupt the curve is on it. Ideal for players with large hands.