Positive / Negative difference between purchase costs of assets and their fair market value depending on accounting standards that are locally applied (some assets like lands or trade receivables remain booked in original accounting value). If any difference as stated above occurs, this is referring to revaluation impairment. Further there can be also revaluation stemming from different currencies for certain assets and liabilities, which also needs to be reflected in the Balance sheet resp. Profit/loss statement. For instance when Company receives a loan in EUR and its local accounting currency is EUR, each year the difference of outstanding amount of this loan recalculated into USD must be booked in the results. 

This represents quite big risk for emerging markets, which have limited liquidity within the local market and need to be funded abroad, so they issue USD/EUR/CHF-denominated Bonds, but the source for repayment are generated in local currencies and therefore if the mutual FX rate changes dramatically and domestic currency weakens then the real nominal amount that is due in foreign currency will increase and may lead to inability for final repayment.