Strong Nash equilibrium
A "Strong Nash equilibrium" is a concept from game theory. Applied to voting theory, it means a set of votes, where no coalition of voters can change their votes to get a result they all prefer. This is one of the strongest, most elusive kinds of equilibria in voting theory. The only ways to make it stronger are if it is known (through some reliable aspect of the system, not just through polling) and/or unique. It has also been called a "Coalition Proof Social Equilibrium" or CPSE.