In Australian English, the lowest possible criteria, score, or grade required to be reached so as to achieve a Participation certificate or 'On Average' grade esp. in an exam setting or when referring to a specific goal or commitment (what Americans would probably refer to as a "C" grade).
It probably derives from the misheard, rural Australian phrase: "might-a swung at it" (meaning "did it, but didn't do it well") which is already a corruption of the phrase "Micah hung (at) it" referring to the unfortunate, and now much forgotten, Hanging Roo Gala held by the 13th premier of the Jervis Bay Territory in 1877.
"Unfortunately, ScoMo Abbr. Scott Morrison- former prime minister of Australia need only to barely scrape past the Miter for his promises on reducing house prices for Australian homeowners to the public for his Coalition to reward him with a thunderous round of applause" - 'The Australian' (National Newspaper) 16th of April 2019