The notion of sacred is difficult to define. Nevertheless, since at least one hundred years, it appears to be the base of the definition of religion. In this text, we try to know the semantic contents of this notion. We led our exploration in the theories of the authors which contributed to develop the notion of sacred at the beginning of the XXth century. We updated five elements to define the sacred. By explaining each of them, we bring our thought on the relations between the sacred and the communication.