[uncountable, countable]a phone service that you can use if you call somebody and their phone is being used, so that your phone will ring when the line is free; a call made using this service
[uncountable, countable](computing计算机)a process by which the user of a computer or phone system proves their identity by contacting a computer, which then contacts them回叫（指计算机或电话系统用户通过连接某台计算机证实自己的身份，然后该系统对之进行回调）
[countable](especially North American English)an occasion when you are asked to return somewhere, for example for a second interview when you are trying to get a job（对求职者等的）召回