Family law is subject to rules both big and small, so that your case moves along in a fair, orderly way. Service of process is one of these rules, ensuring that you can't get a divorce or ask the court to decide something for you without giving your spouse or the other party a chance to defend himself in the legal action. The phrases, "return of process" or "return of service" relate to how you let the court know that you served the other party with a copy of the papers you filed with the court.
Service of Process
In some states, you can ask an acquaintance to deliver your papers for you -- you just can't do so yourself. Other states allow you to give them to the other party if he signs a voluntary acknowledgment of service. Or, you may be able to send the papers to him by certified mail or have the county sheriff or a private process server deliver them for you. The important thing is that the other party to your case receives a copy in a way that's permissible under your state's laws.
Providing Proof to the Court
After the other party receives your papers, you must let the court know that you achieved service. You can file the certified mail receipt or the acknowledgment of service if your spouse voluntarily accepted the papers from you. If you use the sheriff or a private process server, these individuals typically sign an affidavit stating that they personally gave the papers to the specified party. You can then file this document with the court.