Detail
DN is the LDAP Distinguished Namedn: uid=aerospike,ou=People,dc=field,dc=aerospike,dc=com
Answer
It is a string that uniquely identifies an entry in the LDAP directory.
Additional info about DN definition can be found on this LDAP WIKI page.
It consists of a uid, an OU Organizational Unit and a DC Domain Components.
Note that in the Aerospike config file, any spaces in the DN must be escaped. See the Parameters Whose Values Must Be Escaped documentation page for the list of characters that must be escaped.
example:
query-user-dn uid=aerospike,ou=Trusted/20User,dc=field,dc=aerospike,dc=com