It's the amount of memory allocation in bit.
By default many systems allocate 1048576 bit (1 Megabit).
/* Example 1 */
class Test {}
$classTest = new Test();
$reflectionClass = new \ReflectionClass('Test');
$classModifiers = $reflectionClass->getModifiers();
var_export($classModifiers);
//output
1048576
/* Example 2 */
class Test {}
//the constructor is missing
$reflectionClass = new \ReflectionClass('Test');
$classModifiers = $reflectionClass->getModifiers();
var_export($classModifiers);
//output
0
