1. Order size refers to the number of shares bought or sold, which can be a round lot of 100 shares (or multiples of 100) or an odd lot of 1-99 shares. 2. Time limits on orders specify how long an order is valid, such as one day, week, or month. Open orders remain open until filled or cancelled, while fill-or-kill and discretionary orders give brokers flexibility in execution. 3. Short selling allows investors to borrow and sell securities they do not own, hoping to purchase them later at a lower price. It carries higher risk than long positions as losses are unlimited.