Revaluation means a change of a price of goods or products. This term is specially used as revaluation of a currency, where it means a rise of currency to the relation with a foreign currency in a fixed exchange rate. In floating exchange rate correct term would be appreciation. Altering the face value of a currency without changing its foreign exchange rate is a redenomination, not a revaluation.
In general terms, revaluation of a currency is a calculated adjustment to a country's official exchange rate relative to a chosen baseline. The baseline can be anything from wage rates to the price of gold to a foreign currency. In a fixed exchange rate regime, only a decision by a country's government (i.e. central bank) can alter the official value of the currency. Contrast to "devaluation".
For example, suppose a government has set 10 units of its currency equal to one US dollar. To revalue, the government might change the rate to five units per dollar. This would result in that currency being twice as expensive to people buying that currency with U.S. dollars than previously and the US dollar costing half as much to those buying it with foreign currency.
Before the Chinese government revalued the yuan, it was pegged to the US dollar. It is now pegged to a basket of world currencies.
Tax revaluation is the adjustment of the tax level to slow or stop the rise in tax-revenue as the price of a taxable asset increases. This is considered a fiscally conservative measure to encourage spending. One common usage is the tax revaluation of real estate property to counter a rise in land value. This way, even as property values rise (whether due to increased demand, better government services, or inflation), residents and businesses still pay the same amount of money.