Reference: Regulation (EU) No 965/2012 on Air Operations, Annex I (Definitions) and Annex III (Part-ORO)
The term 'Sterile Flight Deck' is used to describe any period of time when the flight crew members shall not be disturbed e.g. by cabin crew, except for matters critical to the safe operation of the aircraft and/or the safety of the occupants. In addition, during these periods of time the flight crew members should focus on their essential operational activities without being disturbed by non-flight related matters, i.e. flight crew members should avoid non-essential conversations, should not make non-safety related announcements towards the passengers, etc.
Sterile flight deck procedures are meant to increase the flight crew members' attention to their essential operational activities when their focused alert is needed, i.e. during critical phases of flight (take-off, landing, etc.), during taxiing and below 10 000 feet (except for cruise flight).
The sterile flight deck procedures were published in Regulation (EU) 2015/140 as an amending regulation to (EU) No 965/2012 on air operations. EASA published the associated AMC and GM with ED Decision 2015/005/R.