Lot

What it is:

A lot is a securities trade for a “standard” number of trading units. In stock trading, a lot is 100 shares (also called a "round lot"). However, inactive stocks generally trade in 10-share lots.

How it works/Example:

Lots are the standard trading amount, and thus they usually incur the most favorable commission costs. For example, if you wanted to buy six lots of Company XYZ stock, you would be buying 600 shares.

Investors, especially individuals, frequently cannot or do not want to bear the expense of trading shares in round lots, however, which is why most brokers also accept “odd-lot” trades (though they may charge a higher commission for doing so). However, the advent of electronic and online trading platforms has reduced, and in some cases eliminated, these odd-lot premiums.

Why it Matters:

Lot  investors tend to be larger investors. The ratio of odd-lot buying to odd-lot selling, on the other hand, is often used to evaluate small-investor sentiment.

Best execution refers to the imperative that a broker, market maker, or other agent acting on behalf of an investor is obligated to execute the investor's order in a way that is most advantageous to the investor rather than the agent.