In the context I used it, ldap = username

Essentially all employees have a unique account that is used for email, unix sysadmin, etc., and this is accomplished via LDAP. You can sync permissions, auth, and more between various systems if they all speak the same language.

To use our hacker news usernames, yours would be "pdmccormick" and mine would be "echelon". Companies may choose to make these based on personal names, but it's not required.