Ad-hoc means playing with people that have DFF and are in ten meter range.
Ad-hoc Party means playing with people online via a PS3 and the AHP program.
XLink Kai means playing with people online via a computer, the XLink Kai program and a WiFi USB Adapter.
Anyway.
Dissidia Forums has hosted three tournaments (and is currently hosting one) over Ad-Hoc Party. It has also hosted a XLink Kai tournament and is currently hosting another one as well. So yeah. If you want DFF tourneys, you know where to go.
There have been several other tourneys hosted on other sites like GameFAQs as well.
Thanks Sho Minamimoto Couldn't have explained it better if I googled it.