What's a Topic?
http://helpstuff.com/blog/index.php/2008/08/12/what_s_a_topic

Helpstuff
2008

Abstract:

Back in 1998, I defined topics as "'chunks' of information in a Help file that answer one question or provide focused, specific content." Ten years later, I typically use the same definition. However, there have been some changes in how those "chunks" are developed.