As we all know Multiple Select in HTML is a Select box where we can choose multiple values.
While define multiple select by adding multiple=”multiple” like the example below –
But when we will submit data, even after choosing multiple values, $_POST will show only one entry. To get all the values we need to change the name from sel to sel. This will result in showing all the chosen values in $_POST like below –
[sel] => Array
 => 1
 => 2