negative externality An undesirable impact of a transaction between two parties (individuals, business firms, government) upon a third, uninvolved individual or group. Related Related Articles: Where and Why We Fly (Less)Why Traffic Jams Could Spread LessThe Downside of an Airplane’s DescentThe iPhone: What We Didn’t Know We Wanted1930s Noise Pollution Ann Mills Share This Previous ArticleM1 Next Articleopen market operations December 17, 2020