From (Court ruling)
http://www.ntsb.gov/alj/o_n_o/docs/AVIATION/3655.PDF
The FAA Administrator in his reply brief concedes that the regulation (FAR section 91.71(d) defines acrobatic flight as "...an intentional maneuver involving an abrupt change in an aircraft's attitude, an abnormal attitude, or abnormal acceleration, not necessary for normal flight.") does not define acrobatic flight in terms of specific degrees of pitch or banking, but asserts that such specificity is unnecessary and would be undesirable, given the wide variation in aircraft and their design capabilities.
Australia has much the same
Civil Aviation Regulation 2 acrobatic flight means manoeuvres intentionally performed by an aircraft involving an abrupt change in its attitude, an abnormal attitude, or an abnormal variation in speed.
but goes on to say
Civil Aviation Regulation 155 Acrobatic flight
(2) For the purposes of subregulation (1), straight and steady stalls or turns in which the angle of bank does not exceed 60 degrees shall be deemed not to be acrobatic flight.