Definition and background:
The techniques involved by musicians to provide air to a wind instruments. The techniques, although similar for all wind instruments, have unique aspects for each instrument. Combined with the techniques of tonguing and embouchure, breathing is a critical aspect of instrumental tone production. Some of the special breathing techniques include staggered breathing and circular breathing.See also staggered breathing and circular breathing.
In the audio world, this is the audible change in level of a signal due to the use of noise reduction or other dynamics processing.
For more information on the music term "Breathing" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary