In the IVR, there are several states or statuses. This article explains the difference between them.
Returns a counter of agents that are in the tested campaign that are idle and ready to take a call right now. so you can go Ready Agents >= 1 means that SOME agent is ready to take a call RIGHT NOW.
Returns a counter of agents that are in the test campaign that are idle, or working. So You can allow a call in and to queue knowing that an agent is going to finish what they are doing and then be there to take the call. There's someone manning the queue actively (not eating lunch etc)
Idle Agents (Ready to Handle Calls)
Returns a list of agent Ids that get counted in "Ready Agents". The operator here is contains or does not contain. The purpose is looking for a specific agent. Is Agent Jane ready to take this call right now. Note that the Queue Node allows for specifying queueing to a specific agent which is what you might follow this with.
Available Agents (logged in and active)
Returns a list of agent Ids that get counted in "Available Agents". Works similar to Idle Agents (Ready to Handle Calls). Is Agent Jane currently working this queue so I can queue a call specifically for her when she is done with what she is doing now.
Returns a counter of agents that are ready to take a call now OR are currently in an outbound call that is still in a ringing state. On an outbound dial, if the phone is still ringing, and the other person has not picked up yet, that call CAN be interrupted (hung up suddenly and bringing the agent back to available) to allow the agent to take an inbound call that would be considered more important. Note that this checks for bargability, but does not do the barge itself. That is controlled by the call entering the queue and the flags set that allow barging to occur.