Was at last able to haul out the paperwork and find, from the Australian AIP ENR 60_1, the definition sought by 737incognito, which is:
An aeroplane's reference field length is:
(1) in the case of an aeroplane to which section 20.7.1B of the Civil Aviation Orders applies (see below but basically civil turbines & jets) – the balanced field length; or
(2) in the case of any other aeroplane – the take-off distance; that the aeroplane requires for take-off in accordance with subpara b. below:
b. For the purposes of sub-para a. (1) and (2) above, the balanced field length or take-off distance that an aeroplane requires for take-off is the balanced field length or take-off distance that, according to its flight manual, the aeroplane requires:
(i) on a level runway,
(ii) at maximum take-off weight,
(iii) in still air,
(iv)at sea level, and
(v) in standard atmospheric conditions.
Section 20.7.1B of the Civil Aviation Orders says:
Subject to paragraph 2.2, this section applies to:
(a) all turbine powered aeroplanes having a maximum take-off weight in
excess of 5 700 kg; and
(b) all new types of piston engine aeroplanes having a maximum take-off
weight in excess of 5 700 kg placed on the Register after 1 June 1963.
2.2 For paragraph 2.1:
(a) a certificate of airworthiness for the aircraft must be in force; and
(b) the certificate must include a statement to the effect that the certificate is issued in the transport, commuter or normal category.