Are there any HTML hidden values I can use

I added a button on my webpage so a host and a client can have a meeting. Very simple, I love it. I was wondering if there are any values I can pass through the php $_POST buffer to control the program. In HTML these would be the <input type=‘hidden’ … > type of parameters. I’m not looking for anything specific at this time but if there are any options available I would like to be able to take advantage of them.