Because 丨 a 丨 =a, when a=0, 丨 0 丨 =0, so the absolute value of zero is still zero.

Absolute value is the distance from a point corresponding to a number on the exponential axis to the origin, which is represented by "||". |b-a| or |a-b| represents the distance between the point representing a and the point representing b on the number axis. The absolute value of a number can be considered as the distance from zero.

The absolute value of a positive number or zero is itself, and the absolute value of a negative number is its inverse.

The generalization of absolute value of real number appears in various mathematical settings, such as complex number, quaternion, ordered ring, field and vector space to define absolute value. Absolute value is closely related to concepts such as size, distance and norm in various mathematical and physical environments.