Ad hoc mediation refers to a mediation process that is arranged on an informal, case-by-case basis, rather than being part of a formal mediation program or system. It typically involves a mediator who is selected specifically for a particular dispute and who works with the parties involved to help them reach a resolution. Ad hoc mediation can be a flexible and cost-effective way to resolve conflicts, particularly when the parties prefer a more informal and customized approach to mediation.