Most basically it is simply relaxation. More advanced meditators might address and process anything whatsoever in meditation. It is a very good idea to help clients to be able to meditate by themselves. It puts them more at cause, it makes them more responsive to their own internal signals, and it makes them more able to step out of the noise of everyday living. Meditation is processing.
Typical meditation consists of a simple recursive technique.
The basic rules of processing apply. It is therefore a good idea to introduce the client to some of these principles. Such as, staying on one subject at a time, staying involved, finishing what one starts, not judging what comes up, etc.