Definition
Plain language
A situation in a game where no player can do better by changing their move alone.
As stated in the literature
A solution concept in game theory where each player's strategy is a best response to the others', so no unilateral deviation improves payoff.
Also called: Nash
Why it matters: It's the standard way to predict stable behavior in strategic interactions, from auctions to multi-agent AI systems.
For example, in rock-paper-scissors, playing each move with probability one-third is a Nash equilibrium because switching unilaterally doesn't help.
Heard on the show
“So what does it actually replace Nash with?”Episode 234 — Two Copies of Gemini Cooperated in a Game Where Betrayal Always Pays