The method attribute of the HTML <form> tag tells how the form data is sent to the server. There are two values: GET and POST. If you write nothing, the default is GET.
<form>
<form method="get" action="search.php"> <!-- fields --> </form> <form method="post" action="login.php"> <!-- fields --> </form>
$_GET
$_POST
The details are in difference between GET and POST and PHP Forms Handling.