Web applications are independent of the operating system of the terminal / end device. The applications are being opened via internet browser. Simply expressed web applications are websites with a significant higher interactive value.
In addition the data can also be acceded on any other device, from any location with internet access, if the URL and - where required - user name and password are known. Web applications are mostly responsive. Meaning they are optimized for all screen sizes and as easy to use on a personal computer as on a tablet.