In message-oriented middleware solutions, fan-out is a messaging pattern used to model an information exchange that implies the delivery (or spreading) of a message to one or multiple destinations possibly in parallel, and not halting the process that executes the messaging to wait for any response to that message.[1][2][3]

In software construction, the fan-out of a class or method is the number of other classes used by that class or the number of other methods called by that method.[4]