Accumulated income is that portion of a corporations' net profits that are retained, rather than being remitted to investors as dividends. The aggregate amount of accumulated income appears in the retained earnings section of the balance sheet.
A business needs accumulated income to help fund its operations. This is especially important for a growing business, which typically requires a substantial amount of working capital to pay for its ongoing investments in receivables and inventory, as well as fixed asset purchases.
The amount of accumulated income tends to be lowest in slow-growth businesses, where the management team has no internal use for the money and so elects to send it to investors in the form of dividends.