The absolute value of a number is its distance from zero on the number line, regardless of direction. It is always a non-negative value. For example, the absolute value of both 3 and -3 is 3, since both are three units away from zero. In mathematical notation, the absolute value is represented by two vertical bars. For instance, |x| denotes the absolute value of x. This concept is useful in various fields, including mathematics, physics, and engineering, as it helps to simplify calculations involving distances and magnitudes.