HTML hypertext markup language.
hypertext: (linear) text that has links to other texts, forming a web of interconnected documents.
markup language: notation that indicates the structure of a document.

HTTP hypertext transport protocol.
protocol: the rules and message formats used by networked computers to communicate.
HTTP is the part of the Internet protocols (TCP/IP) used by web browser (client) and web server to get web pages.
Browser sends a Request to a server for a "resource", server sends the Reply with the resource.

URL: universal resource locator. Internet address.
http://serverName/folder/Path/filename
protocol://serverNameOrIPaddress:port/path/to/folder/or/file
with all parts being optional.
Protocol is HTTP by default.
Port is 80 by default. Sometimes 8000 or 8080 is used for a caching web server.
Secure, encrypted HTTP is protocol https:// which uses port 443.

Web page Layers

0. content (text & images)
1. structure: HTML. What it is.
   • block-level elements: paras, headings, lists etc
   • inline elements: img, em, a (links) etc.
   • HTML 5 structural elements: section, article, nav, aside, header, footer
   • generic elements: div, span
2. presentation: CSS. How it looks, how the elements are laid out.
   • text formatting: colors, fonts, sizes
   • margins, borders, padding, color, background images of blocks
   • positioning & page layout
3. behavior. How it interacts, if any.
   • Javascript: part of the page
   • client-side: Java applet, Flash
   • server-side programs: ASP, Java, PHP etc. Typically interact with a database.