APN (Access Point Name)
Updated
An APN (Access Point Name) is the name a cellular device sends to the mobile network to say which packet data network it wants to reach. The network uses it to pick the gateway, the IP addressing and the routing for the data session. Its format, a network identifier followed by an operator identifier, is defined by 3GPP.
In practice
With an IoT SIM, the APN decides where your data goes: a public APN leads to the internet, a private APN leads only to your own network or cloud. Most devices let you set the APN by SMS command, AT command or configuration app.