I've been browsing the documentation relentlessly, but I just can't seem to figure out what it's called when a function uses an argument which has an int datatype. For example, in filter_var:
filter_var('bob@example.com', FILTER_VALIDATE_EMAIL);
... or in curl
curl_setopt($curl, CURLOPT_URL, 'http://example.com');
What is FILTER_VALIDATE_EMAIL and CURLOPT_URL called?
They are called Constants.
It just a variable, but because it is constant it should be written as Capital letters just to distinguish from other types of variables.That's the naming convention.
define('YOUR_CONSTANT', '894616466');
echo YOUR_CONSTANT;//894616466
These are called "Predefined Constants". They're published by category i.e.