الْبَدَلُ is the noun used to substitute the fore-mentioned noun in the succeeding sentence. The substitute must follow the word for which it is substituted. The substitute is called الْبَدَلُ, and the substituted is called الْمُبْدَلُ مِنْهُ. Example: فَآمِنُوا بِاللَّـهِ وَرَسُولِهِ النَّبِيِّ الْأُمِّيِّ  So believe in Allah and His Messenger, the unlettered prophet (7:158)