Message Bus

A Message Bus is a messaging infrastructure to allow different systems to communicate through a shared set of interfaces(message bus).

Source: EIP

Message Queue

The basic idea of a message queue is a simple one:

• Two (or more) processes can exchange information via access to a common system message queue.

• The sending process places via some (OS) message-passing module a message onto a queue which can be read by another process

Source: Dave Marshall

Difference

Message Queue contains FIFO(first in first out) rule whereas in Message Bus does not.

Conclusion

Both LOOK like doing same kind of work - passing messages between two Applications or Modules or Interfaces or Systems or Processes, except small difference of FIFO