Smarts
Skill Rank Maximum is the representation of a Character's limits in regard to learning skills in general, there is only so far a Character can take their general knowledge without either applying it to specifics, or just plain becoming smarter.
Skill Rank Maximum is the maximum amount of Ranks that may be gained in any given Skill.
Example: A Character with 2 Smarts could only ever have 2 ranks in Athletics, Tech, or any other Skill, even during [Character Creation].