Trac has a built-in wiki engine, used for text and documentation throughout the system. WikiFormatting is used in wiki pages, tickets and check-in log messages. This allows for formatted text and hyperlinks in and between all Trac modules.
Editing wiki text is easy, using any web browser and a simple formatting system, rather than more complex markup languages like HTML. The reasoning behind its design is that HTML, with its large collection of nestable tags, is too complicated to allow fast-paced editing, and distracts from the actual content of the pages. Note though that Trac also supports HTML, reStructuredText and Textile as alternative markup formats.
The main goal of the wiki is to make editing text easier and encourage people to contribute and annotate text content for a project.
The wiki itself does not enforce any structure, but rather resembles a stack of empty sheets of paper, where you can organize information and documentation as you see fit, and later reorganize if necessary.
Some more information about wiki on the web: