This function works just like rand() but faster and with a “more random” result.

The “mt” stands for Mersenne Twister which is a pseudorandom number generating algorithm developed in the late 1990s.

// results will vary, of course
$n = mt_rand();          // 684257369
$n = mt_rand();          // 1838824035
$n = mt_rand( 17, 403 ); // 48
$n = mt_rand( -55, -2 ); // -54
See the manual entry for mt_rand()