Green’s Dictionary of Slang

1. a wrinkly sheep.

1899		Brisbane Courier (Qld) 24 Nov. 7/7: A wrinkly sheep is a ‘leatherhead’ and a ‘concertina’.
1906		Register (Adelaide) 13 June 8/6: one gentleman made reference to the imported Vermont ram as the ‘concertina sheep’.
1941		Western Mail (Perth) 7 Aug. 21s/3: The grand champ[ions in those days were ‘concertina sheep’ with masses of wrinkles from head to toe.
1970		J.S. Gunn in Ramson Eng. Transported 65: A concertina, a slang term for a wrinkly sheep is now also a side of lamb in some places [AND].

2. a side of lamb or mutton.

1897		Bulletin ( Sydney) 7 Aug. Red Page: Ribs of Mutton — ‘Concertina’. Ancient, and very common throughout Australia.
1945		Baker Aus. Lang. 80: Concertina, a side of mutton.

3. a style of leggings with wrinkles in them; orginally worn by 19C NSW Mounted Police and drovers.

1895		Advertiser (Adelaide) 5 Apr. 16/6: A young man in a wild state of excitement and ‘concertina’ leggings rushed into the [...] office.
1908		Queenslander (Brisbane) 22 Feb. 44/1: I say, Beatrice [...] your ‘concertinas’ are at half-mast [...] She grabbed the cheap open-work abominations and tried to haul them up a bit.
1934		Argus (Melbourne) 20 Dec. 13/7: Twenty-three pairs of concertina leggings sold for 9/- a pair.
1947		E. Hill Flying Doctor Calling 19: There are leggings, spring-side or concertina — concertina are the most comfortable, but if you get them wet you can’t take them off for six weeks so spring-side are recommended [AND].
1951		Morn. Bulletin (Rockhampton, Qld) 2 Mar. 5/2: Is it possible that somebody [...] may have [...] a pair of concertina legings to sell?
1975		R. Edwards Aus. Traditional Bush Crafts 82: R.M. Williams describes concertina leggings as, ‘A stockman’s style that is as old as Australia and one of the best’ [AND].
1994		Aus. Biography Project 9 Feb. 🌐 We go back to bowyangs and concertina leggings [...] things like that.