Copied from another thread:
Headstock offset means that the headstock's top and back surfaces are moved straight down vertically, usually by 1/8" to 1/4". This creates a radiused curve or "scoop" of the top surface up to where the nut is.
Most Gibson headstocks have zero offset. The headstock is tilted back, but the top surface is a flat plane right up to the nut.
Here's a quick comparison from my image files. The headstock in the foreground is 7 degree angle with only a tiny bit of offset. The headstock in the background is also 7 degree angle, but with 1/4" offset. You can see how adding the offset lowers down the inboard tuners. It also makes the access hole for the truss rod better.
These were guitar neck blanks that I made for Mike Lipe many years ago. We experimented with different combinations of headstock angle and offset, and that's the combination we liked best and used in production: 7 degrees and 1/4" offset. This provided good string break angle geometry for all of the tuners, and kept the angle reasonable for strength and fitting in cases. I made about 800 instrument necks like that for Mike.
By the way, you can also add offset to flat (no tilt angle, Fender-style) headstocks. A stock Fender headstock is considered to be zero offset; there's no angle, and the back surface of the headstock is in a flat plane with the heel surface. An improvement on the Fender design is to offset the headstock down by 1/8" or even 1/4", still keeping it flat (no angle). This improves the string break angle over the nut without needing any retainers, and still keeping that flat headstock look. I've added that offset on many custom flat-headstock necks in the past.
