Hosted Fields is a flexible and customizable solution provided by Braintree which allows accepting credit card payments using their JavaScript SDK. When the hosted fields are used, the sensitive payment inputs are being rendered using iframes in your web page. The hosted fields solution is used by Jotform Braintree integration. With hosted fields, the payment data is securely sent directly to Braintree, so it is never stored on Jotform servers.
You can check out Drop-in vs. Hosted Fields in the referred page.