Re: Topics vs Categories
Taking the bigger item first, Categories are used to organize all kinds of objects at a Tikiwiki site. These objects can include wiki pages, blogs, galleries, and articles. See Categories.
Topics are the way articles (only) are categorized. These in fact function as categories but are not the same as the overall Tiki Categories. Articles can also be Categorized, though, if you want all articles of a certain kind (topic) brought into a Tiki Category. See Articles.
(Adding further to the name confusion, Tiki's Directory for web site listings also uses "categories" for its hierarchy of URLs, and these are also not the same as Tiki Categories, but can be Categorized. 
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-- Gary
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