Symbols consisting of mathematical symbols "L" and "anti-L" (that is, anti-L) usually represent absolute values. This symbol is called vertical line symbol or absolute value symbol.

Absolute value is a positive value, which is used to indicate the size of a number (the absolute value of a number). When a number is positive or zero, its absolute value is equal to itself; When a number is negative, its absolute value is equal to its opposite number (minus sign is removed).

The absolute value is expressed as follows:

-If x is a real number, its absolute value is symbolically represented as |x|, for example |3| = 3, |-5| = 5.

The sign of the absolute value can be regarded as the way that two vertical lines "|" surround a number to represent the absolute value.

For example, if there is a number x = -4, then |x| = |-4| = 4, and its absolute value is 4. Whether x is positive, negative or zero, its absolute value is always non-negative.