INF
Infinite is a PHP constant, called INF. It is also possible to generate such a value, with calls to math functions such as log(0) or 1e308 * 2.
While the infinite is a float, it is possible to test a number with is_infinite().
<?php
$infinite = 1e308 * 2;
var_dump(is_infinite($infinite)); // true
var_dump(INF === $infinite); // true
echo str_repeat('1', 1000) + 0; // INF
?>