The tv-wikilinks variable controls the behaviour of the $link widget.
The widget normally produces a link to a tiddler. But if this variable has the value no, the widget suppresses the link and simply displays the text that would otherwise have served as the link.
You can suppress links for a whole tiddler by placing the following line at the start of the tiddler's text:
\define tv-wikilinks() no
This variable has no effect on external links, as those do not involve the $link widget.