Meaning

noun erect bushy annual widely cultivated in warm regions of India and Indonesia and United States for forage and especially its edible seeds; chief source of bean sprouts used in Chinese cookery; sometime

originOften doubtfully explained as mash until no good, or a self-referencing (recursive) acronym, mung until no good. Rumored to have originated from one of the Massachusetts Institute of Technology computer groups in the 1970s or 1980s. Potentially related to mangle.

Etymology from Wiktionary, CC BY-SA 3.0