The Greek Old Testament would translate it as "so be it". Literally it means 'fixed' or 'sure'. I use it myself as a closing to my own prayers as a means of showing respect and thanks.
If Amen is? This is not really a question but I assume that what you really mean is "What is Amen? If this is what you mean then here is your answer. Amen is a word said at the end of prayers such as...