Transmission of one or more signals from one organism to another.
Note that it is the stimulus that is transmitted whereas it is reception of the signal that constitutes communication. This communication need not be intentional, need not be two way, and need not result in the recipient responding to the signal for communication to have occurred.
If reception of the stimulus does not occur, however, then communication has not occurred. may indeed make a , but it hasn't communicated that sound unless some animal hears it!