When, through their own fault, a pair is unable to play a board, the tournament director will usually award it an average minus (40% of the total matchpoints available). For an innocent pair unable to play a board, the award would be average plus (60% of the total or its overall percentage score for the session, if better).
The words ‘average plus’ and ‘average minus’ are also general terms to denote scores slightly above and below average. If the scores on a board are +420 (several times) and +170 (once), then all the pairs with 420 could say they have an average plus score on the board, while all those sitting the other way with -420 could say they have an average minus score.