Financial performance is measured by profit or loss. Profit is measured as income less expenses. Income include both revenue and gains.
Revenue is income arising in the course of ordinary activities of the entity. It include sales revenue, fee income, royalties income, rental income and income from investments (interest and dividends).
Gain include gains from disposal of non current assets. Realized gains are often reported in the financial statements net of related expenses. They may arise in the normal course of business activities. Gains may also be unrealized. Unrealized gains occur when an asset is revalued upwards, but is not disposed off. For example, an unrealized gains occur when marketable securities owned by entity are revalued upwards.