A memorial service is a service without the remains present and can vary in ceremony and procedures according to the community and religious affiliations. Some families prefer public visitations or gatherings followed by a private or graveside service with a memorial service later at a House of Worship or other location.
Because the remains is not present at the memorial, final disposition may take place either before or after the service. You can have a memorial celebration instead of a traditional service, or in addition to it. For instance, you might have a traditional funeral service in the town where the person lived and died, and a memorial service later in the town where he/she grew up.