Absolute Value: if x is negative, then |x| = -x

Dear Greg Mat and everyone!

I just red the ETS Math review guide, there’s a sentence about absolute value that says:
“if x is negative, then |x| = -x”

I understand that absolute value means the distance between x and 0, but I just can’t understand what the sentence means.

I hope someone can explain it to me :smiley: