Application Function (AF)

AF is a node where apps run on. For example if you work for a utility company, then that company may own its own AF. Or run your application on the AF of a hosting company. That AF is registered at the telecommunication operator and allowed to execute services for certain set of devices. AF as a hub may help to run operator-agnostic, cross-border services.

AF is an HTTP client and server. There is nothing special in that regard.

For development purposes such service may run on your laptop. Or on a highly available public cloud service.

In some documents you may run into the term SCS/AS. That is essentially the same as AF. That term is inherited from 4G IoT. In contrast, most Telephony APIs do not use the term AF, but "application" instead, and related request paths do not contain AF ID.

AF is an IoT concept of owning resources. For telephony services AF and Apps are equal.