This is a read-write value naming a Dialer Number Identification Service (DNIS) map, a mechanism for grouping and identifying called-party numbers, that's associated with this voice peer entry. An admin uses this to apply a shared set of DNIS-based routing or classification rules across multiple called numbers via a single named map rather than configuring each number individually. For example, an admin managing a large range of DID numbers for one department could group them all under a single DNIS map name referenced here instead of creating a separate peer for each number.