ACTION
Action, Call to Action or in general terms, a button on a landing page
Call now, click here, download it now, share this are the typical call to actions found on a landing page.
Taking action is the ultimate goal of the landing page. It is what you want your visitors to do in response to your offer.
Your form headline generally contains your offer and the button is the call to action. This makes form the epicenter of your landing page. Consider your form to be a mini landing page which has the capability of converting even if everything else is removed.
Like the headline, your call to action should be clear, benefit oriented and action centric. It should be asking to get clicked.
Since it is the goal of the landing page, it should be easily discoverable ( with contrasting colors and above the page scroll)