In guitar anatomy the headstock is a part of the neck, the part being all of the neck located between the nut and the end of the neck not meeting the body. The headstock exists as a place to locate the tuners. Almost all guitars, be they electric or acoustic, Dobro, Bass guitars, have a headstock - there are a handful of models that do without it through some type of ingenuity.

Different headstock shapes are used by brands to distinguish themselves - some strat copies look exactly the same as a Fender save for the headstock.

The traditional headstock, as seen on classical guitars, is often referred to as a 3 + 3 configuration as 3 tuners are located on the top and 3 on the bottom.

What follows a breakdown of guitar writeups by headstock type, based on my own knowledge, the writeups themselves and any updates I receive. (/msg sud with updates)

Guitars with 3 + 3 headstocks:

Guitars with all tuners on the top: