[lhoff]

That stands for HTTP Strict Transport Security. Its a http header that basically tells your browser to only connect to this website via HTTPS/TLS for a configurable amount of time.

Its a protection mechanism that prevents encryption stripping man-in-the-middle attacks.

[jbverschoor]

I know, that's why I mentioned it. The http site worked fine for me, so I figured parent post already has a HSTS entry in his browser