Absolute value is the magnitude of a number, regardless of whether it is positive or negative. Another way of putting it is that the absolute value of a number is its distance from zero on a number line. Therefore, -6 and 6 have the same absolute value: 6. And even though -6 is less than 4, the absolute value of -6 is greater than the absolute value of 4.
The mathematical symbol for absolute value is a set of vertical lines around the number in question, as for instance |6| or |-6|. If the negative sign is inside the absolute value lines, then the answer will be positive. However, if there is a negative sign outside the lines, the answer will be negative, as in -|8| = -8 or -|-8| = -8.