Syntax: radio button choice
The Categories Type setting sets what type of categories are being used, and how to optimize category searches. It set to one of:
Auto-detectAutomatically detect what kind of categories are being used at search time, and optimize searches accordingly. This lets non-overlapping categories (i.e. those whose pages do not occur in any other category) be searched fastest, while still supporting overlapping categories as fast as possible. This is the default mode.
OverlappingAssume that any category might overlap another. Category searches will be slower than with the other modes. This mode was used before the Categories Type setting existed. It can be set as a fallback if the cached overlap data is believed to be incorrect for some reason, e.g. category searches are wrong.
Non-overlappingAssume that no category overlaps another. All category searches will be as fast as the fastest
Auto-detectmode search, but searches for overlapping categories may not show all results. This mode can be set to force higher-performance searches at the potential expense of accuracy.
See the tips and performance caveats on the main Categories page (here).