RTMP is a TCP-based protocol which maintains persistent connections and allows low-latency communication. To deliver streams smoothly and transmit as much information as possible, it splits streams into fragments, and their size is negotiated dynamically between the client and server. 

A Pull RTMP (Real-Time Messaging Protocol)  link is a playable link of your live stream, which you can set up as a source in another broadcast.

The pullRTMP feature allows you to play one live stream inside the other. You can have an original stream playing in the background and you can add graphic overlays with the audio commentary in the foreground. 

PullRTMP is especially useful when you want to have multiple live streams from Field or Remote Location to Studio