"Declaration (beyan)" that is a concept in Koran means "explanation, articulation and making apparent" in the dictionaries. After Koran became a book and the apocalypse period was far away, the term "beyan" lost its meaning like many words in the Qur'an. We see that loss of meaning occurred when the concept beyan was deemed to mean" to expound that is succinct". However, based on our findings, it is recognized that the concept beyan does not mean" to expound that is succinct" when we examine the poetry in the apocalypse period and when we read the relevant verses within the integrity of the Koran and taking their context into consideration. In this respect, we can say that loss of meaning occurred regarding the meaning of the concept beyan. According to the results of our work, when the In Koran, the base "b-y-n" and its derivatives used in various patterns mean "divine explanations". Beyan in the meaning of declaration of the prophets is to deliver the respondents the apocalypse taught into their hearts by the God as it is without hiding it, adding something to it, changing it and forgetting it.