https://www.bleepingcomputer.com/news/security/new-tsuname-dns-bug-allows-attackers-to-ddos-authoritative-dns-servers/

Attackers can use a newly disclosed domain name server (DNS) vulnerability publicly known as TsuNAME as an amplification vector in large-scale reflection-based distributed denial of service (DDoS) attacks targeting authoritative DNS servers.

In simpler terms, authoritative DNS servers translate web domains to IP addresses and pass this info to recursive DNS servers that get queried by regular users' web browsers when trying to connect to a specific website.