Absolute Value  -  The absolute value of a number a, denoted |a|, is the positive distance between the number and zero on the number line. It is the value of the corresponding "unsigned" number -- that is, the number with the sign removed.

Boundary Point  -  A value of the variable that makes the equation true when an equal sign is substituted for an inequality sign (<, ≤, >, or ≥). Also called a critical point.

Critical Point  -  A value of the variable that makes the equation true when an equal sign is substituted for an inequality sign (<, ≤, >, or ≥). Also called a boundary point.