Definition of 'Form 1099-B'
A form issued by a broker or barter exchange that summarizes the proceeds of all stock transactions. The sale of a stock will be accompanied by a gain or loss, which must be reported to the IRS when you file your taxes. Specifically, figures from form 1099-B are used on IRS Form 1040, Schedule D.
Brokers are required to provide you form 1099-B by January 31.
Investopedia explains 'Form 1099-B'
For example, let's assume you sold several stocks within the last year and the proceeds of the transactions equal a capital gain of $10,000. The amount gained from the sale of the stocks will be issued in form 1099-B by your broker and this amount must be included when you file your income taxes.