"Center Squeeze" refers to a class of voting scenarios which are troublesome for many voting systems. In such a scenario, the strongest three candidates can be arranged on a spectrum such as "left", "center", and "right"; and of the three, the "center" candidate is the Condorcet winner but the honest Plurality loser (that is, the one with the fewest voters strictly preferring them over the other two). Most consider that if the centrist is not too far behind in honest plurality, they should be the winner, as otherwise the voting system is encouraging strategy (typically, a favorite betrayal) from one of the other two groups.
Voting systems which have serious problems with center squeeze include IRV and two-round runoff voting. Systems which can do either well or poorly in a center squeeze situation include most graded Bucklin systems and score voting. Systems which generally do well with center squeeze include Condorcet systems (although in some cases, a center squeeze scenario could become an opportunity for one of the wings to use burial strategy and create an artificial Condorcet cycle).