The standard unit of trading in a particular type of security. For stocks, a round lot is 100 shares or a multiple thereof, although a few inactive issues trade in units of 10 shares. For corporate, municipal, and government bonds, a round lot is usually considered to be $100,000 of principal amount of securities per trade. Customers involved in securities transactions in lots other than round lots are often penalized somewhat because the trades require more broker and dealer effort. Also called even lot, normal trading unit. Compare odd lot. See also lot.