CASA’s Flight Operations Regulations - Consolidated Dictionary is fairly clear although some of my friends choose to twist the words to give a different meaning.
“flying in formation
2 or more aircraft are:
(a) flying in formation if they:
(i) are operating as a single unit with regard to navigation, position reporting and control; and
(ii) are so close to each other that any change in height, heading or airspeed of any aircraft used for station-keeping results in a need for one or more of the other aircraft to manoeuvre to maintain station or avoid a collision; and
(b) taken to be flying in formation:
(i) when the aircraft are changing station; and
(ii) during join-up or breakaway.”