How about this...
"In Labview, you build a user interfaceby using a set of tools and objects. The user interface is known as the front panel. You then add code using graphical representations of functions to control the front panel objects. The block diagram contains this code. If organised properly, the block diagram resembles a flow chart."
The UI & block diagram together form a VI (Virtual Instrument) that may be recursively used in other VI's to build complete applications.
(the part in quotes is a direct copy from the NI 'getting started with Labview' manual