What means Reinvestment reserve?

When a business asset is disposed of, the book profit for tax purposes may, under certain conditions, remain outside the annual taxable profit. It can then be (temporarily) placed in a reserve for future reinvestment. It is necessary for an intention to reinvest to exist and to take place within 3 years. The reserve and the reinvested investments must be written off against the investment, resulting in a lower book value.