• a WikiTopic has a distinct WikiWord title that defines it; a Web page doesn't
• a topic's content is self-contained, doesn't spill over onto other topics; a Web page can continue a subject, book-like, across many pages
• particularly in TWiki, a topic has an array of features that make it distinct - attachments, relationships to other topics, classification data, independent revision control, and so on; a Web page has none of that

A topic is used by TWiki to generate a regular Web page.

-- TWiki:Main.MikeMannix - 12 May 2002