In the context of VoIP (and WebRTC), bitrate is the number of bits per second that are being actively sent or received over the network.

A few things to remember about bitrate:

• The maximum bitrate possible is capped by the bandwidth available, which can be dynamic throughout a single session. See BWE
• Bitrate changes dynamically throughout the session, due to a multitude of reasons: available bandwidth, CPU, etc.
• Voice codecs require much less bitrate than video codecs
• Downstream and upstream bitrates are asymmetric