Extensions enable you to modify your Microsoft Dynamics NAV system without directly altering the source resources, making it easier to deploy, manage, and upgrade customizations or extensions.
While you will still use the existing Microsoft Dynamics NAV Development system to customize or extend Microsoft Dynamics NAV, a new set of Windows PowerShell cmdlets have been introduced that mean you can add your changes into a proprietary package format, called a .navx package file.
These packages can be installed, and more importantly uninstalled, from a Microsoft Dynamics NAV system with ease.
Packages can be automatically upgraded through the installation process, so up taking newer versions is made easier.
For the time being for more details see : Introducing Extensions in Microsoft Dynamics NAV 2016
Will come up with more details in my upcoming posts.