Greek or anal sex is of course penetration of the anus. It can be a intense and highly pleasurable experience for both parties, but must be approached with care and understanding.
Part of the excitement of anal is the taboo surrounding it, so both you and your partner have to be totally in agreement that it can take place and totally relaxed both mentally and physically.
Plenty of lubrication is necessary to recreate the fluids normally available during conventional sex, and entry has to be achieved gradually and very slowly to avoid damaging the anal canal. If these measures of care are taken, the result can be amazingly erotic and satisfying for both you and your escort.
However, don’t expect every escort to be willing to accept anal. Make sure before your booking that this is a service she is willing to provide, and be respectful during your meeting if she decides that it isn’t going to take place for whatever reason.