It stands for accumulated other comprehensive income; the amount of other comprehensive income (OCI) that is accumulated by a firm over a period of time. Accumulated other comprehensive income includes unrealized gains and losses (related to certain investments, pension plans, and hedging transactions) reported under stockholders’ equity (in the balance sheet). It is displayed on the balance sheet to highlight potential realization of gains/ losses on the income statement in the future. For example, the unrealized loss on available-for-sale securities would be closed out to the account of other comprehensive income at the end of financial period.

The effect of accumulation is calculated over the course of the period:

Accumulated other comprehensive income (ending) = other comprehensive income + accumulated other comprehensive income (beginning)