The full meaning of DNS is the Domain Naming System, while the meaning of LDAP is the Lightweight Directly Access Protocol. DNS simply refers to the adopted naming system in hierarchical order, which is used for computers, services, on a private network, or secondary resources connected to the internet.
The DNS stores an IP address, and equates domain names to it, after which you will be directed to a web address, then to a device, provided it is connected to the internet. On the other hand, LDAP serves the purpose of maintaining and accessing directory information that is distributed over what is called an IP, which is Internet Protocol.
Certificate handling is another major difference between DNS and LDAP. DNS can only be updated manually, unlike LDAP, which has an option where you can add, rename entries, and also delete. The DNS is more widely used, and also easier to use than LDAP.