Is "angostura" (as in bitters) a flavor? I'm confused by drink recipes calling for "Angosutra bitters".  Is "angostura" (as in bitters) a specific flavor combination?  

Or is "Angosutra" a specific brand or manufacturer (like "Tylenol" is to aspirin)?  If so, what's the closest possible replacement for it?
Angostura Bitters is a specific brand of bitters.  The Angostura in the name refers to the town where it was originally produced.