ECC has a lot of disconnect reasons that may require an explanation. Here is a pass at that.
Unknown: We don't know -- we did not or could not assign a disconnect reason for some reason.
Disconnect: The call ended, and no more specific disconnect reason could be determined. If an agent handles a call to completion the disconnect reason will be disconnect because the call ends. Less commonly a call in queue can end with "Disconnect" if a script terminates the call, for example.
Transfer: The current party transferred the call to another party. Most commonly agents doing transfers to other agents.
Abandoned: Caller hung up while in queue or while ringing to an agent. ECC logs a specific "Abandon" event to CCIR when a call is abandoned. If the call ends while in queue and there is no "Abandon" event the reason will be "Disconnect" instead.
AgentAnswered: An agent in the group answered the call.
OtherAnswered: An agent in a different group answered the call. If a call is in multiple groups simultaneously as a result of overflow, the group in which the call was answered will be "AgentAnswered" and all the other groups will be "OtherAnswered".
PresentedNotAnswered: When a call rings to an agent and they do not answer it, the disconnect reason for that agent will be "PresentedNotAnswered".
ReEntered: The call re-entered ECC routing via a new IRN. Typically the result of a script action or call routing destination where the target is an IRN. Except interflow, which is noted specifically.
Interflow: The call was routed by interflow rules on the service to a new destination. This will always take precedence over other disconnect reasons when applicable (e.g. ReEntered, PBXTransfer).
CallbackRequested: The call ended because the caller requested a callback via a callback script.
BecameNonACD: The call was an ACD call in queue or ringing to an agent, but started ringing to or was answered by an agent as a non-ACD call. Possible examples are an agent performing a pickup on another agent's ringing phone, or a script action directing a call directly to an agent's extension.
PBXTransfer: The call was transferred out of ECC to a destination in the PBX. Examples would be an agent transferring a call on to a another PBX destination or a script action directing the call to a non-ECC destination (a "leave a message" option for example).