An odd lot refers to an amount that's less than the typical number of shares or units you'd trade for an asset.

In stock trading, an odd lot would describe any amount less than 100 shares of a stock, which is considered a standard – or "round" – trading unit.

Only the commission per share differs when trading odd lots. You can trade an odd lot in your portfolio like any other asset.

A primary reason why you may find an odd lot in your portfolio is that the company did a reverse split.

A reverse split is when the company reduces the number of outstanding shares, thereby increasing each share's value.

Suppose each share was worth $10, and the trading firm you were using charged a 1% commission based on a minimum trade size of 100 shares.

That means if you sell 200 of your original 300 shares, you will end up paying 1% of $2,000 – or $20 for the trade.

Suppose you wanted to sell 66.7 percent of your shares, or 33 shares. If your broker's odd-lot policy still requires 100 shares, you'd pay $10 to sell 33 shares after the reverse split. You'd pay 10% of the $1,000 minimum lot size, or $10.