Labels are objects that float above the terrain (usually) and display
some text message to the user.  They're primarily used in 3D map sort of
application.  In other words, they're not intended to be real world objects.
You would use one if you want to float a message such as "Natural History Museum"
over a specific building in a visual database.

They point to a font name to be used for the text displayed. The txp loader will look
for fontmap.txt file in the txp archive directory in which font name to font file name
map should be provided since osg uses freetype for the Text displayed and there is no
interface to create fonts based on their name (or at least I was not able to find it :) .. )
 - it uses the font file name instead

Ex:
Times New Roman = times.ttf
Arial = arial.ttf  
Arial Narrow = arian.ttf 
Courier New = cour.ttf