[iTunes] Where is iTunes stored?

[Ron Michael]

Probably a dumb question but I'm getting ready to re-organize my iTunes 
library (I hope). I've built some playlists in iTunes but a lot of my 
tunes are just spread around in there willy-nilly. Where are my tunes 
actually stored on my hard drive. In other words, what is the default 
location? Once I complete my organization, do I still need to keep the 
actual, original downloads or will the iTunes folder suffice? I know I 
should probably safe the originals but hard drive space may be a 
problem in the future. If I want to backup the important iTunes stuff 
in case of a hard drive tragedy, what folders do I keep as a backup?
Thanks.
Ron in Memphis