A huff is an active breath out, used to move mucus towards the mouth where it can be easily cleared with a cough.
A huff is done with an o-shaped mouth and open throat. It is an active breath out, an active sigh, as if trying to fog up a mirror.
Once children are old enough, huffs should be part of all airway clearance routines and should be taught by the CF physiotherapist.
It can also be called a forced expiratory technique (FET)