The modulus function is

Note that $|x|\geq 0$ for any real $x$, and $-|x|\leq x\leq|x|.$ Some computers use the term absolute function or ${\hbox{abs}}(x)$ for the modulus function. The idea is that $|x|$ measures the absolute size of the real number $x$, and that $|x-y|$ measures the distance between points $x$ and $y$ on the real line.