Domain generation algorithms (DGAs) are used to auto-generate domains, typically in large numbers within the context of establishing a malicious command-and-control (C2) communications channel. DGA-based malware (such as Pushdo, BankPatch, and CryptoLocker) limit the number of domains from being blocked by hiding the location of their active C2 servers within a large number of possible suspects, and can be algorithmically generated based on factors such as time of day, cryptographic keys, or other unique values.
https://docs.paloaltonetworks.com/pan-os/9-0/pan-os-admin/threat-prevention/dns- security/domain-generation-algorithm-detection