Final answer:
Domiciliary service means that a copy of the summons and complaint can be left at the usual place of living with a person 18 years or older and mentally competent.
Step-by-step explanation:
Domiciliary service, under the federal rules for process service, allows the copy of the summons and complaint to be left at the usual place of living with a person who is 18 years or older and mentally competent. This means that someone who is at least 18 years old and able to understand the legal documents can accept the service on behalf of the defendant.