MIA is a military acronym which stands for Missing In Action. A soldier who is MIA is unaccounted for, it is not known whether the soldier is dead, taken prisoner, has deserted or is wounded or lost in the terrain. MIA is a designated status that actually means that the status of the soldier is unknown. MIA is used as a noun and as an adjective. With the advent of ID tags in World War I it became easier to assign casualty statuses, meaning fewer soldiers were permanently designated as MIA. MIA has also come to be used as slang to describe anyone who is not where he should be, such as at his desk in an office. Note that MIA is rendered without periods.
Examples
But they are finally getting some long-awaited closure after the Defense POW/MIA Accounting Agency recently recovered and identified the remains of Dudley Evans. (The Advocate)
The Department of Defense POW/MIA Accounting Agency, based in Hawaii, working jointly with the Kingdom of Cambodia, went back to the scene of the crash several times, and in February 2012 witnesses identified a single burial site that contained remains from the three missing soldiers, the agency’s website states. (The Bangor Daily News)
Mother of Soldier Missing in Gaza Wants Him Declared MIA, Not Dead (Haaretz)
In extreme cases, such as a man who is declared MIA, it follows that the wife is not allowed by the state to annull the marriage and remarry if she wishes. (The Jerusalem Post)
He said he was about 16 years old and at school when he was told his brother had been designated MIA. (The Bellevue Leader)
Victorian contestant Laura, who entered with her brother Mitch, has apparently gone MIA. (The Courier Mail)