A naked domain (Bare domain) is simply a domain name without the 'www' prefix. For example, google.com (naked) instead of www.google.com (full) Most websites map their naked domain to be forwarded to their www (full) address.
Incapsula offers a naked domain to www. Rediraction to all of our customers; you can find it in your site's dashboard on Settings => General => Redirection.
For additional information, see also: Domain Redirection Feature.