PEP stands for Positive Expiratory Pressure.
Oscillating PEP is also known as vibrating PEP.
Oscillating PEP involves breathing out against resistance, a bit like breathing through a straw and creating vibrations in the device that are then transmitted into the airways.
Breathing against the resistance helps to splint the airways and hold them open, allowing air to get in behind the mucus, making it easier to move towards the mouth.
The oscillations or vibrations help to shake the mucus off the airway walls and break the sputum up making it easier to shift.
Resistance and oscillations can be created in many different ways, using water, a mouthpiece or a mask.