O seguinte comentário de esquema INetOrgPerson do OpenLDAP fornece uma explicação simples:
# displayName
# When displaying an entry, especially within a one-line summary list, it
# is useful to be able to identify a name to be used. Since other attri-
# bute types such as 'cn' are multivalued, an additional attribute type is
# needed. Display name is defined for this purpose.
Espero que ajude:)