Basically, a distinction is made between DAB+ and internet radio even though both convert digital information back into sound. For DAB+, the stations need special transmitters to broadcast the signal. This signal has a geographical range depending on the transmission power. There is also no two-way connection between the transmitters and the receivers.
This is also referred to as one-to-many broadcasting. A transmitter can be received by any number of devices within its transmission area. But the transmission areas are limited in the radius around the transmitter. The receiving devices do not communicate back to the transmitter.
For internet radio, an internet connection between the transmitter and the receiver, is actually necessary. So-called streaming servers are used for this purpose. The receivers or listeners connect directly to these servers via the streaming URL. The capacity of a server always has a technical limit, called slots, so the number of simultaneous listeners is limited.
The large web radios do not only use one streaming server, but have flexible networks that can also serve many simultaneous listeners. There is actually a two-way connection between the sender and the receiver. The streaming server can technically count how many devices are currently connected. There is no classic broadcasting area, either. Internet radio can be received around the globe as long as an internet connection can be established.