The $ID value of an item may be used as a special designator for single items or groups.
For example:
$Name(1524673590) locates the $Name of the note whose $ID is 1524673590.
$Name(1524673590;1524673572) locates the $Name of the two notes whose $IDs are listed.
Note that this particular designator usage should be avoided whenever possible, as it is hard to read and thus confusing for the occasional user. However it is made available because in some circumstances it may be the only practical way to reference item(s) where relying on unique paths are impractical.