Queue Manager
A queue manager, such as WebSphere MQ Queue Manager, acts as an intermediary between the programs that want to exchange information. It functions as a server, controlling the flow of information in and out of a set of queues. Queues reside on the queue manager and you can associate multiple queues with one queue manager.
The programs that want to communicate with one another (whether they are the suppliers of information or the consumers of information) are the Queue Manager's clients. Because these programs do not interact directly, they are considered peers of one another. Under this architecture, one program is not subordinate to, or a client of, the other.
Note:
The Queue Manager does not actively process or distribute the messages it receives. Its role is to simply accept messages and hold them in the appropriate queue until a client explicitly requests them.