Meaning
It is found singly and sometimes doubly at the end of prayers (Ps 41:13; 72:19; 89:52), to confirm the words and invoke the fulfilment of them. It is used in token of being bound by an oath (Num 5:22; Deut 27:15-26; Neh 5:13; 8:6; 1Chr 16:36). In the primitive churches it was common for the general audience to say "Amen" at the close of the prayer (1Cor 14:16).
The promises of God are Amen; i.e., they are all true and sure (2Cor 1:20).