jQuery CDN is a way to include jQuery in your website without actually downloading and keeping it your website's folder.

jQuery is a JavaScript library which is a free, open-source software designed to simplify HTML DOM tree traversal and manipulation, as well as event handling, CSS animation, and Ajax.

cdnjs is a free distributed JS library delivery service.

Cloudflare is a web-infrastructure and website-security company, providing content-delivery-network services, DDoS mitigation, Internet security, and distributed domain-name-server services.

Ubuntu is a free and open-source operating system on Linux for the enterprise server, desktop, cloud, and IoT.

Apache is a free and open-source cross-platform web server software.

Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.

Varnish is a reverse caching proxy.