A webpage is a collection of hypertext markups (aka HTML) and plain text used to allow a virtually platformless display of information.
For a webpage to include images, colors, or anything beyond simple text, it uses a set of instructions, or tags that the web browser viewing the page is free to ignore, or follow to access images, colors, formatting, and other various affects.
Because a webpage is, in and of itself, nothing but text, computer incapable of displaying various types of media that may be referenced (sound, animations, images, color, particular fonts, etc) can discard those references and just display what they are able to. A well designed page will still be pleasant to look at, and to work with, on systems that can display nothing more than the text. Or, will provide an alternate page designed for such systems.
Webpages can be part of a website, and can be either personal, commercial, or government pages. Pages are referenced with a URL or Uniform Resource Location (also known as a web address).