When a package is created, it is put under /usr/ports/packages/All and links are made from one or more subdirectories of /usr/ports/packages. The names of these subdirectories are specified by the variable CATEGORIES. It is intended to make life easier for the user when he is wading through the pile of packages on the FTP site or the CDROM. Please take a look at the existing categories and pick the ones that are suitable for your port.
This list also determines where in the ports tree the port is imported. If you put more than one category here, it is assumed that the port files will be put in the subdirectory with the name in the first category. See the categories section for more discussion about how to pick the right categories.
If your port truly belongs to something that is different from all the existing ones, you can even create a new category name. In that case, please send mail to the FreeBSD ports mailing list <freebsd-ports@FreeBSD.org> to propose a new category.