DNIS, Dialed Number Identification Service, identifies the number the caller dialed. A business running several numbers, one per product, campaign, or location, uses DNIS to route each to the right team and greeting.
It is the inbound counterpart to caller ID. Where ANI says who is calling, DNIS says which of your numbers they called.
Frontdesk uses the dialed number to apply the right greeting, knowledge, and routing automatically, so each line behaves the way you set it.