Can the global $_POST variable be set from another website?

For security reasons, i always check things in the database and all, but i there's several things i wouldn't need to check if only my website could use the $_POST variable of my website.

So, to wrap it up, can i create a form in a website like (website1.com) and set the form action of another website (website2.com)?

Example: I have the following form in my website1.com:

    <form method="post" action="website2.com/something...">
        .
        .
        .
    </form>

Would my form be able to send the $_POST variable with some information to the other website?