what does abs() means in c++ code example

Example 1: abs c++

#include <stdlib.h>     /* abs */

int main ()
{
  int n,m;
  n=abs(23); // n=23
  m=abs(-11); // m=11
  return 0;
}

Example 2: abs in c++

[Mathematics] |x| = abs(x) [C++ Programming]