What is/are the difference(s) between revenues and gains?

Revenue is the amount earned from a company's main activities such as selling merchandise or providing services.A gain results from a peripheral activity, such as selling the old delivery truck. A gain is the amount received that is in excess of the asset's carrying amount (book value). For example, if the company receives $3,000 for the truck, and its carry amount was $600, the company will report a gain of $2,400.