God Stat
A God Stat is roleplaying gamer slang for a character statistic with a particularly unbalanced effect compared to the other characteristics. It is the opposite of a Dump Stat. God stats are often accidentally created by GMs as a result of their house rules; sometimes, however, they are present in the system RAW. In combat-related games it is typically the stat that governs the number of attacks or actions-per-round the character is allowe.
Dexterity/Agility is the most common god stat in combat-oriented games, often allowing one to hit more, be hit less, and move faster.
Examples
In Inquisitor, a Warhammer 40,000 RPG and skirmish-level wargame, the godstat is Speed, a stat derived from Initiative, as this gives more actions/attacks per turn.
In Mage: The Ascension, the God Stat is literally Arete; it's a measure of how enlightened the character is with their godlike ability to defy the cosmos. It sets the upper-limit to a Mage's magic powers, and high Arete means a Mage can use magic without wasting time with foci or rituals. Maxxing it out won't make you overpowered, but one point of Arete is worth more than one point of anything else.
In Mekton, Reflex is the God Stat because without it you simply can't do anything awesome (like be a Mechwarrior, which is what the system is built around) and you will just fall over a lot and get hit all the time (like your average grunt suit pilot - NPCs should have low Reflex.) It's closely followed by Intelligence and Education, which govern your number of skill points. High numbers of skill points allow you to add a fuckton to dice rolls, since they're nearly all opposed checks using Reflex and at least one skill.
In the Fallout series of games, the undisputed god stat is intelligence. Having a high intelligence gives you the most skill points, so it would be retarded to neglect it.