The expression "x | x < 2" represents a mathematical condition where the variable x can take any value that is less than 2. This means that x can be any number from negative infinity up to, but not including, 2. For example, values like 1.5, 0, and -3 all satisfy this condition. In this context, the vertical bar "|" indicates that we are defining a set of values for x. This notation is often used in set theory and inequalities to specify constraints on the variable. Thus, the set of all possible values for x is x | x < 2.