APN is an abbreviation for Access Point Name. It refers to a setting on mobile phones that identifies an external network the phone has to access for data.
Without the right Access Point Name settings, a phone cannot send multimedia messages (MMS) or connect to the Internet via the mobile network. The APN is usually configured or detected automatically by a smartphone or tablet, meaning users don't have to manually make changes to the APN settings on their device in order to get data service. APNs are usually stored in contexts that are identified by number, and they specify how to establish a data session.