An ordinary dividend is a distribution of corporate earnings that is taxed at the shareholder's ordinary income tax rates, the same graduated rates that apply to a paycheck. It stands in contrast to a qualified dividend, which meets specific conditions that let it be taxed instead at the lower long-term capital gains rates. "Ordinary" here refers to the tax treatment, not to how common or plain the dividend is; a large, routine dividend from a blue-chip company is usually qualified, while a dividend from a real estate investment trust is usually ordinary.
The term also has a precise meaning on the tax form. Form 1099-DIV, which brokers and funds send each year, reports "total ordinary dividends" in Box 1a. This is the gross figure, and it is easy to misread: Box 1a includes everything, and Box 1b, "qualified dividends," reports the portion of the Box 1a amount that is eligible for the reduced rates. The IRS instructions state that Box 1b is "the portion of the dividends in box 1a that qualifies for the reduced capital gains rates." So the two boxes do not add together. The qualified amount is a subset of the ordinary total, and the portion taxed at ordinary rates is Box 1a minus Box 1b.