Mya is an abbreviation used by geologists and paleontologists for "Million Years Ago". Other less than obvious abbreviations that might be encountered in similar contexts are BP (Before Present), TYA (Thousand years ago), Gya (Gigayears ago -- i.e a thousand million years), BCE (Before Christian Era = BC in common usage), and the somewhat Americentric Bya (Billion Years Ago. == thousand million years = Gya).
