Some DNS background.
The DNS is a system of managing domains and IP addresses. It has a specific tree-like structure built with hierarchy. For administrative purposes and to make the whole system more manageable and decentralized, it uses delegated partitions called DNS zone. The DNS zone is a part of the Domain namespace that has its autonomy of management.
What is a DNS zone file?
Each of the delegated partitions called DNS zones has a DNS zone file where the DNS administrator for each zone can add instruction, settings, authentication mechanisms, and more for the zone. They are in the form of DNS records – simple text instructions that other computers and sometimes people can read and understand.
DNS zone file format explained in detail