Plain English Meaning
A catch-all section in the navigation database for useful background information that doesn't belong in any of the main categories. It holds reference data the system needs but that isn't a single point you fly to.
Full Definition
In the ARINC 424 navigation database specification, miscellaneous records are a category of data records used to store reference and supporting information that does not fit into the primary navigation record types such as airport, runway, navaid, waypoint, or airway records. They typically include items like cruising tables, geographical reference tables, FIR/UIR boundaries, restrictive airspace, grid MORA values, and similar supplementary data that supports flight planning and navigation but is not itself a navigable feature.