What is "openldap"

Openldap is open source software that implements the LDAP protocol. It is a directory service based on the X.500 standard. It has the standard files called schemas. Sungaila (2008) states that "a schema is a set of rules that defines attributes, object classes, and controls indicating where each data can be stored". Malère (2008) explains a schema as being an object structure that specifies the total list of attributes allowed and required for a data entry in the directory service. Schemas allow you to maintain data consistency. An important feature of these files is that they are extensible and so you can add more attributes or classes depending on needs.

Source:http://pt.wikipedia.org/wiki/OpenLDAP