Fazluddin is an Arabic name for boys that means excellence of the faith, superiority of the faith, meaning the person named such is a righteous person.
Fazlurrahman is an Arabic name for boys that means Gods bounty, Gods excellence, Gods generosity, meaning that the person named such is a gift from God. ar-Rahman is a synonym of Allah (God) and literally means the most majestic, the most merciful.
Fehredin is the Turkish variant of the Arabic boy name name Fakhr al Din, which means pride of the faith, most brilliant among the believers. They are the same name and have the same meaning.