HSTS
In plain terms
A policy forcing browsers to use HTTPS for a site.
Going deeper
HTTP Strict Transport Security tells browsers to only connect over HTTPS, preventing downgrade and SSL-stripping attacks. It enforces encryption.
Under the hood
Delivered via a response header; preload lists hardcode HSTS into browsers for first-visit protection.
Examples
Web security, HTTPS enforcement, Strict-Transport-Security header, preload.
Think of it like...
Like a permanent rule that visitors must always use the secure, locked entrance.