Skills routing and ACD · foundation · 12 min full read
Wikipedia describes an automatic call distributor as a telephony device that answers and distributes incoming calls to a group of terminals or agents. It says the route can depend on the caller's number, the number dialed, the time of day, or an answer to a voice prompt, and that an advanced system may take input from CTI, CSTA, or an IVR.
The Five9 skill groups chapter is the queue this lab could read. It says skill groups organize users who have the agent or supervisor role into groups assigned to the call queues that are part of campaigns. That is the Five9 object. The Wikipedia article is the general word ACD. Do not treat them as the same paragraph.