"Many skills offer specialization in specific aspects of the skill purchased as a talent."
I was able to figure this out, but it was much harder than it should be. I started looking on pg 26 in the main entry describing how skills work. The quote above hints you should look at the talent list, where you finally describe what specialization does on pg 37. It's a pretty obscure link.
Suggestion, pg 26:
"Some skills let you purchase the Specialization talent to get +1 step using certain aspects of the skill. Specializations are listed in the skill descriptions."
On pg 37 you should be clear whether players can buy multiple specializations for the same skill or not. "Each talent may only be purchased once or once per focus." Not clear if each specialization counts as a focus.
I made the first adjustment in v2.5... Thanks
On the second, the "once per focus" rule applies to all talents that have a focus including Specialization. This statement is intended to allow a character to purchase the talent more than once. As the Shoot specializations pistol and rifle would each be a "focus" a character can purchase both, but it wouldn't be particularly efficient as for the 20 Destiny (presuming it exceeds their linked skill, Fortitude), they could have just increased their Shoot a die type.
Scribe of the Adventure System