The key is in the readme.pdf file and on the POI downloads page.
Each entry is categorised by prefixing the wild camping location description as follows:
CR - car park rural
CU - car park urban
LR - layby rural
LU - layby urban
OR - other rural location
OU - other urban location
PH - pub stopover
The prefixes are particularly useful on a satnav to help you choose a location that is suitable for you.
The prefix is followed by the place name.
All descriptions have the county name appended.
If it's a pub stopover, the description includes the pub name after the location name.
If a location is accessed from a dual carriageway, the description includes the direction of travel for access.
Comments have been added where useful. These are only accessible in Google Earth and AutoRoute.