This header entry determines whether a browser is allowed to render a page in a frame or iframe. This can prevent so-called clickjacking attacks by making sure that the website is not embedded in another website. The following options are available:
DENY: The page is not rendered if it is being loaded in a frame or iframe.
SAMEORIGIN: The page is only rendered if the frame or iframe is located in the same domain.
ALLOW-FROM DOMAIN: The page is not rendered if the domain is different from the domain specified here.