An Attribute Score Increase is a point at which a character’s experience warrants a permanent improvement, specifically to one or more of their Attributes. Player Characters may get an optional ASI at the time of Character Inception, in addition to specific ones for race/species and as part of a Feature.
Optional ASI: The character increase a single Attribute by +2 or 2 different Attributes by +1. Unless otherwise noted, an ASI cannot take the character beyond a measure of 20 in an Attribute (“ability”).