Synchronous: The client sends a request and waits for the response. This is the way HTTP is behaving.
Asynchronous: The client does not wait for a response and just sends the request to a message broker. AMQP is an asynchronous protocol.
Single Reciever: Each request is received and processed by a single receiver.
Multiple Receiver: Each request can be processed by zero to multiple receivers. This must be an asynchronous protocol.