With the old-fashioned Microsoft Dynamics NAV ERP (on-premise proposition by Microsoft), the traditional way for customizing the solution is to use the C/SIDE and C/AL languages.
C/SIDE is the standard integrated development environment (IDE) born with the first versions of Microsoft Dynamics NAV. With C/SIDE and the development environment application, you have access to all the NAV objects, and from here you can customize every part of the application:
With C/SIDE and by using the C/AL language, you can create new objects such as Tables, Pages, Codeunits and so on and you can edit standard objects (made by Microsoft) and modify them as to your needs.
With this traditional way of programming, you can write code in new objects and you can write code inside standard objects and inside standard Microsoft code (between lines). Isolation...