When you get to the U’s in the acronym dictionary there’s a traffic jam... URI, URL, URN, where does it end? For now, we’re going to focus on the URLs, or Uniform Resource Locators, that you know and love. Every resource on the web has its own unique address, in the URL format.
Optional Query String: Remember, if this was a GET request, the extra info (parameters) would be appended to the end of this URL, starting with a question mark “?”, and with each parameter (name/value pair) separated by an ampersand “&”.
Well-known TCP port numbers for common server applications
The TCP port numbers from 0 to 1023 are reserved for well-known services (including the Big One we care about—port 80). Don’t use these ports for your own custom server programs!