A story ability is one that Geralt receives during the course of The Witcher (PC) without specifically having to allocate one of the talents he earns (or consume a mutagen). These include two bronze-level attributes:

Talent bronze Potion Brewing, an intelligence upgrade
Talent bronze Flaying, a dexterity upgrade,

and knowledge of the Ritual of Magic when using places of power. The two other rituals can not be performed without allocating talents when levelling up.