Should unavailable options be grayed out or invisible to users?

1. Is it greyed out or grayed out?
2. What is it called when a button is greyed out?

Is it greyed out or grayed out?

Grayed out is the term used for a disabled graphical control element in a graphical user interface. It is often done with a light shade of gray on the specific element. Grayed-out elements help in minimizing confusion for the user regarding an element's status and whether or not it is active or available.

What is it called when a button is greyed out?

isabled or inactive buttons are often “greyed out” — with white or grey text on a grey button. These can be used to communicate to the user that some kind of task needs to be completed by them before they can proceed, such as entering an email address in a text field prior to sign up.