A company you invested in might send you a check instead of crediting a fractional share to your stock account. You might also receive a Form 1099-B at the end of the year with the description of “cash in lieu.” This is for the cash (the check) you received in lieu of receiving a fractional share.
There are different reporting rules depending on why you received the cash.
The company might have sent you cash in lieu of a fractional share after a stock split. Most corporations don’t issue fractional shares when they split a stock. They pay the shareholder cash for the fractional share, and the fractional share is considered sold. So, you’ll receive a 1099-B.