Internet protocols
It's important to know about how your HTML and other assets are delivered from the web server to your user's browser. Much of this is abstracted away and transparent to web development, but it's a good idea to have at least a basic understanding in order to achieve high performance.
TCP/IP
Transmission Control Protocol / Internet Protocol (TCP/IP) is the name for a pair of communication protocols that underpin the internet. IP is the lower-level protocol of the two, and this deals with routing packets to their correct destinations. IP can run on top of many different lower-level protocols (such as Ethernet), and this is where IP addresses come from.
TCP is a layer above IP, and it is concerned with the reliable delivery of packets and flow control. TCP is where ports come from, such as port 80 for HTTP, and port 443 for HTTPS. There is also the User Datagram Protocol (UDP), which can be used instead of TCP, but it provides fewer features.
HTTP runs on top of TCP, and it is...