What is "Gin" in Gin Rummy?

Short Answer
Gin is achieved when all 10 cards in your hand form melds (sets or runs) with zero deadwood (unmatched cards). Going Gin earns a 25-point bonus plus your opponent's deadwood count. Your opponent cannot lay off cards when you go Gin.

Gin vs Knocking

Example

Your hand: 4-5-6♥ (run), 9-9-9♠♦♣ (set), J-Q-K♠ (run). All 10 cards are in melds with 0 deadwood. You call Gin and score 25 points plus whatever deadwood your opponent has.

Gin Scoring

Why Gin is Powerful

Going Gin is strategically superior because: