LDAP refers to Light weight directory access protocol. We make use of this protocol when there is a requirement of more reads and less writes.
Consider an organisation where we have some thousands of employees and we need to authenticate users daily and we will be making almost million requests . In this type of scenarios it is recommended to use LDAP because we will be adding an employee once to the database and the record is updated very rarely . So we are making two or three writes in an year and read requests happen now and then .