Static Modifiers are any number added to a Dice Pool that is not a Result of a rolled Die. The most common Static Modifiers encountered in play include Skills and Ratings, but can also be found in Abilities gained from Races, Jobs or Items.
Example: Brock the Oricalcai has had a rough Encounter and is currently generating an Injury. Oricalcai have a Static Modifier of -10 to Injuries from their Sturdy and Rugged Traits given by Nigh Invincible, so as Brock rolls a Result of 22 they would add that together with their Static Modifier of -10 to get a Total of 12.