An operation object is a single-shot object—that is, it executes its task once and cannot be used to execute it again. You typically execute operations by adding them to an operation queue An NSOperationQueue object is a queue that handles objects of the NSOperation class type. An NSOperation object, simply phrased, represents a single task, including both the data and the code related to the task. The NSOperationQueue handles and manages the execution of all the NSOperation objects (the tasks) that have been added to it.