The property of an operator that says whether a sequence of three or more expressions combined by the operator will be evaluated from left to right (left associative) or right to left (right associative). For example, in Perl, the lazy and operator && is left associative so in the expression:
$i >= 0 && $x[$i] >= 0 && $y[$x[$i]] == 0
the left-most && is evaluated first, whereas = is right associative, so in
$a = $b = 42
the right-most assignment is performed first.