The keyword "Callback" in Agent Request API?

I am working on Agent Request API . The word "callback" is confusing in the given sentence taken from Cisco guide:

"Cisco SocialMiner works in a Contact Center Enterprise (CCE) solution to process the request from its

inception through the delivery of the callback."

I don't understand what is meant by "Callback" in this context written in the following snapshot.

Any help would be appreciated?

As per use of callback API, it allows callback application to send a notification to CCE for an agent to make a voice call to a customer at customer request.

Complete details on callback is shared in below doc ( Chapter 4 ):

https://developer.cisco.com/fileMedia/download/f5daf482-3faa-4427-834d-d4772e25156e

Hope it helps

Regards

Hemant