These are links created by enclosing the page name in brackets. In this case the page name doesn't have to be a WikiName, it can be (almost) any word or phrase. Things like STX formatting (eg single quotes) can be troublesome.

Freeform links are also "fuzzy links": they don't mind what capitalization, punctuation or whitespace you use. See also FuzzyUrls.

Singlular: FreeformLink