HTTP Strict Transport Security allows web Websites to declare that web browsers or other complying user-agents should only interact with it using secure connections (HTTPS), and never via the insecure HTTP protocol.
HTTP Strict Transport Security uses the Strict-Transport-Security HTTP Response Header
HTTP Strict Transport Security defines a mechanism enabling web sites to declare themselves accessible only via secure connections and/or for users to be able to direct their user-agent(s) to interact with given sites only over secure connections. This overall policy is referred to as HTTP Strict Transport Security (HSTS). The policy is declared by websites via the Strict-Transport-Security HTTP HTTP Response HTTP Header Field and/or by other means, such as user-agent configuration, for example.