It's how far a number is from 0.
( ex.) 6 is 6 away from 0 but so is -6; so the absolute value of 6 is 6 and the absolute value of -6 is 6. the symbol "|" is placed on either side to mean absolute value.
(ex.2) |-6| = 6. -|-6|= -6. |6|=6. and -|6|= -6.
if the negative sign is outside of the symbol then the number will always be negative but if there is no negative sign outside of the symbol it will always be positive, even if it looks lile this. |-6| it would still be positive.