Custom Applications give you the ability to assign applications to specific network traffic that would normally look random. It's designed to be a way to identify traffic that would otherwise look random and give it a custom name because you know the traffic belongs to a specific application. For example, UDP port 12345 is net flow traffic from a known virtual desktop. So we could create a custom application called "Virtual Desktop net flow data" with the same settings then all of the data in the GUI for UDP port 12345 will now be labeled as "Virtual Desktop net flow data" instead of "UDP port 12345".
NOTE: Newly created apps only take effect on new flow records. Existing flow records will still hold on to the old application name.
To create a new Custom Application, Navigate to menu -> System -> Custom Apps
From this page click the blue "+" to open the New Custom App menu.
In the Custom App menu enter a Name, Description, the desired Port number, and corresponding Protocol. After that information is entered, click the blue add button in the bottom left of the menu and your new Custom App is successfully created.