Missed calls: When user A invites user B for a conference, if user A is present in the conference but user B never connects to the conference, it is categorized as a missed call. In WebRTC terminology, this would imply that user A has created an offer but not received an answer.
Aborted calls: When user A and user B join a conference and ICE connectivity checks are ongoing, and one of the user leaves, hence terminating the call, this is categorized as an aborted call. In WebRTC terminology, the ICE connectivity state is in checking when the conference is terminated.
This can occur when the set up time is unreasonably long and the user leaves out of frustration, or sometimes as soon as they enter (realise that they started the call with video or have something in the background, etc) and immediately terminate the call before it is set up.
Dropped calls: If all the users successfully establish a connection to each other, the conference is categorised as successful. However, during the call, if the connection drops because of network or infrastructure issues (e.g., loss in network connectivity or media bridge failure or any other reason), resulting in all the users unintentionally disconnecting from the conference, this is categorized as a dropped call.