WikiNames are a shorthand way of describing other pages in the wiki. They have the advantage that they are automatically translated to hyperlinks to the referenced page, so that simply clicking on the name (which is also automatically highlighted) will direct your browser to the referenced page. Thus navigation through the wiki is simple and convenient.
It is important to understand the rules for constructing a WikiName. They are a form of CamelCase, that is, of two or more words strung together without intervening spaces, and with the first letter of each word capitalized. Numbers are also allowed, but not as the first character of the WikiName. Thus Wiki3Name is OK, but 1WikiName is not. (Notice the difference in highlighting of those two examples.) There must also be at least one lower case letter between any two capital letters. Characters such as '.' (full stop), '_' (underscore), and '-' (minus or hypen) are particularly not allowed in WikiNames.
Other examples of valid and invalid WikiNameExamples can be seen in the eponymous page.
Not for the Faint Hearted
However! There are occasions when alternative characters need to be used. Name such as SeamusO'Shannassy with an embedded apostrophe are sometimes to be preferred, rather than just SeamusOShannassy. (Note that neither of these automatically translate to hyperlinks, the first since it has a non-alphanumeric character in it, and the second because it has two adjacent capital letters.) These forms can be used, as long as they are escaped by flagging to the wiki that they are to be treated as hyperlinks. This can be done by enclosing them in double (square) brackets, as so: [[SeamusO'Shannassy]] and [[SeamusOShannassy]], which then appear in the rendered page as SeamusO'Shannassy and SeamusOShannassy.
It must be stressed that first of these should be regarded as exceptions only, because such names break the rules for file names in the underlying Unix system. Unix is very fussy about special characters, and hence these name get translated to special file names, such as SeamusO(27)Shannassy, where the embedded '(27)'* itself uses some special characters! Can you see where this is heading? The special characters in wiki names become even more special names in Unix file names, which then must be escaped even further as SeamusO\(27\)Shannassy, and so on, every time they used and passed around the system. It becomes a nightmare for the file system maintainer!! On the other hand, there is nothing wrong with SeamusOShannassy, as it contains letters only (no special characters), and is perfectly valid as a file name.
So users are encouraged to not use any special characters in wiki names. Stick to alphanumerics as much as possible, and things will run much more smoothly.
* '27' is the hexadecimal representation for the apostrophe.