Divorce mediation is a process in which divorcing spouses try to negotiate an acceptable divorce agreement with the help of a neutral third party: the mediator. The mediator helps the spouses to communicate and negotiate but doesn't make any decisions for them.
Both mediation and arbitration involve a neutral third party who is not a judge. In mediation, the neutral party has no power to make decisions. In arbitration, the neutral third party -- the arbitrator -- listens to the facts and then decides the case, just as a judge would. Although the parties can present evidence and make arguments, they have no say in the final decision.