"backflow" means the reverse flow of a liquid or gas in a pipeline, plumbing system, or any other system where it is not supposed to flow backwards. Full definition
This means the pump kit includes some sort of backflow protector (the UFO - looking things on the tube) or filter between the parts that touch milk and the pump itself. (pumpables.co)
Mitral valve dysplasia is a congenital malformation of the valve that closes between the left atrium and left ventricle to prevent backflow of blood when the heart beats. (ivghospitals.com)
- S1 Pump motor - Breast shield set x 2 - Backflow prevention filters x 2 - AC adapter x 1 - Inbuilt rechargeable battery (can be used plugged in or runs with the battery for about 3 hours on a full charge!) (amazon.co.uk)