An application can accept command line arguments when invoked. This allows the user to send additional information to the application when it is executed.
When an application is launched, the OS passes the command line arguments to the application as a collection of string values, using a white-space as separator.
Applications receive external arguments on a regular basis: when you open a document by clicking on its icon, the OS selects the associated executable program and calls it, sending the full document filename to the program as an argument.
Thinfinity VirtualUI allows you to send external arguments to applications in a transparent way, which works exactly like sending arguments from the command line.