Annum is a Latin noun meaning year. It is the accusative singular of the second declension masculine noun annus (nominative), anni (genitive) [1]. * Per annum means "occurring every year". * Kilo-annum, usually abbreviated as ka, is a unit of time equal to one thousand years. * Mega-annum, usually abbreviated as Ma, is a unit of time equal to one million (106) years. It is commonly used in scientific disciplines such as geology, paleontology, and celestial mechanics to signify very long time periods in the past. For example, the dinosaur species Tyrannosaurus rex flourished approximately 65 Ma (65 million years) ago (ago may not always be mentioned; if the quantity is specified while not explicitly discussing a duration, one can assume that "ago" is implied; "mya" includes "ago