2.5.5.5 is found in the schema for the regarding attribute. This OID is described in the Microsoft Active Directory Technical Specification MSADTS. 2.5.5.5 corresponds with the basic 1.3.6.1.4.1.1466.115.121.1.26 syntax.[2]
2.5.5.5 is, as far as LDAPWiki can determine, exclusively used in Microsoft Active Directory.