Tiddlers are classified as system tiddlers if their title starts with the special string
$:/. The only difference from ordinary tiddlers is that they are hidden from most searches and lists in the sidebar. (In particular, system tiddlers are shown in the "More/System" list).
System tiddlers provide a simple way to hide the internal components of TiddlyWiki so that they don't clutter things up, getting in the way of the users content.
Many of the system tiddlers follow the convention of using further slashes to delineate the components of the title. For example:
You don't need to create your own system tiddlers, but it can be useful when customising TiddlyWiki. For example, if you create a custom palette you might call it
$:/_MyPalette so that (a) it is hidden from searches/lists and (b) it will appear at the top of the system tiddler list for easy reference.