The traditional caller ID name service, in which a terminating carrier looks up a short name associated with the calling number in a database and displays it.
CNAM predates STIR/SHAKEN by decades. The name is not sent with the call; instead, the terminating carrier performs a "dip" against a CNAM database using the calling number and displays whatever name is stored there. Display names are traditionally limited to 15 characters, which is why so many business names appear abbreviated.
The number holder, or its carrier, is responsible for registering and updating the name in the relevant databases. Because there are several databases and not every terminating carrier queries the same one, a name updated in one place may take time to appear, or may never appear, on some networks.
CNAM offers no cryptographic protection. A spoofed call using a legitimate business number can still pull that business's registered name, which is one reason the industry has moved toward signed alternatives such as Rich Call Data. CNAM remains widely used, however, and many terminating networks combine a CNAM lookup with verification results and analytics when deciding what to show the person being called.
Why it matters to carriers
Customers still notice when their outbound calls show the wrong name or none at all, and they will raise it with you. Keeping CNAM registrations current for the numbers you assign, and knowing which databases your terminating partners use, avoids a steady stream of support tickets and complements newer branded calling efforts.