Accumulation

In the context of corporate finance, refers to profits that are added to the capital base of the company rather than paid out as dividends. See: Accumulated profits tax.
In the context of investments, refers to the purchase by an institutional broker of a large number of shares over a period of time in order to avoid pushing the price of that share up.
In the context of mutual funds, refers to the regular investing of a fixed amount while reinvesting dividends and capital gains.