Dynamic groups specify a filter and all entries that match the filter are members of the group. These groups are dynamic because membership is defined each time the filter is evaluated.
Imagine, for example, that all management employees and their assistants were situated on the 3rd floor of your building, and that the room number of each employee commenced with the number of the floor. If you wanted to create a group containing just the employees on the third floor, you could use the room number to define just these employees, as shown in the following illustration.
The following LDIF extract shows how the members of this dynamic group would be defined.
dn: cn=3rd Floor, ou=Groups, dc=example,dc=com ... memberURL: ldap:///dc=example,dc=com??sub?(roomnumber=3*)