A system that routes interactions based on an algorithm which determines the best available agent for an interaction

ACD (automatic call distribution) is the contact center art and science of getting the right call to the right person as quickly as possible. Genesys Cloud ACD dynamically matches customer interactions and agents, processing and assigning interactions to the appropriate agent.
ACD is a standard contact center term used to reference the system, device, or entity that automatically assigns waiting interactions to available agents using routing rules. ACD calls are associated with a queue.
Non-ACD calls are not associated with a queue.

https://help.mypurecloud.com/articles/about-interaction-routing/
https://help.mypurecloud.com/glossary/acd-automatic-call-distributor/