The notation for taking the absolute value is two vertical lines on either side of the expression being evaluated. Typically, the absolute value notation is used in an expression like this:

In plain language, this means “take the absolute value of negative ”. More generally, the absolute value notation means to take the absolute value of everything within the vertical bars as shown below.

When computing, the absolute value function is used to compute the absolute value of an expression. To see examples of the absolute value operators see this page.