Fastly is a cloud computing services provider. Fastly's cloud platform provides a content delivery network, Internet security services, load balancing, and video & streaming services.
GitHub Pages is a static site hosting service.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
Varnish is a reverse caching proxy.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.