Learn in the textbookFundamentals of Access Control and Network Defense Devices
DefinitionCallback (コールバック) is a method in which the system ends an incoming connection over a telephone line or similar and then itself dials a registered number to connect.
ExplanationBecause the system only calls numbers registered in advance, a third party who has stolen an ID and password still cannot complete a connection from somewhere else. Since the system places the call, it also pays the call charges.
AnalogyIt is like ignoring calls from unknown numbers and instead ringing back a number in your contacts to ask what they wanted.
Memory hookThe name is the everyday phrase, as in “I'll call you back.”