HSTS (short for HTTP Strict Transport Security) is an internet security standard that serves to redirect browsers to connect only using secure HTTP connection (HTTPS) and not with the insecure HTTP protocol.
This option protects against secure protocol downgrade attacks and cookie hijacking for Force.com sites and communities using the default Force.com subdomain that connects using HTTPS.
HSTS is enabled by default on Visualforce pages, and you can choose to activate or deactivate HSTS for Force.com sites and communities. You cannot deactivate HSTS for Visualforce pages.
Let's take a look at redirections in the next section.
