What is "strategyproofness"

In game theory, an asymmetric game where players have private information is said to be strategyproof (SP) if it is a weakly- dominant strategy for every player to reveal his/her private information, i.e you fare best or at least not worse by being truthful, regardless of what the others do.

SP is also called truthful or dominant-strategy-incentive-compatible (DSIC), to distinguish it from other kinds of incentive compatibility.

An SP game is not always immune to collusion, but its robust variants are; with group strategyproofness no group of people can collude to misreport their preferences in a way that makes every member better of, and with strong group strategyproofness no group of people can collude to misreport their preferences in a way that makes at least one member of the group better off without making any of the remaining members worse of.