A web page is
a computer data file that can include names, words, messages, pictures, sounds, and links to other information. Every web page has its own web site, which is its address, similar to a telephone number or street address. 
Web pages may contain "graphics and text that contain ‘links’ to other pages -- either within the same set of data files (‘Web site’) or within data files located on other computer networks.”  In addition, much of the page may not “reside” anywhere, but be generated “on the fly” under the control of computer programs (written in programming languages such as “Java”).
The HTML source of a Web page is text that defines the content and format of a page. In addition to the graphical representation provided to the viewer, the page may contain additional information related to its author, programming code, metadata, and other identifying information that may not be displayed in Web page view.