What contitutes income in accounting terminologies? Does income encompass both revenue and gain?

Income is the end result of activities that a business carries out. It encompasses revenue and Gain.

"The International Accounting Standards Board (IASB) uses the following definition: "Income is increases in economic benefits during the accounting period in the form of inflows or enhancements of assets or decreases of liabilities that result in increases in equity, other than those relating to contributions from equity participants."

Revenue is Operating income ie.income from normal course of business activities in which an organisation is engaged in.It is recurring in nature. ie.Sale of goods or services

Gain is Non-operating income ie. not from normal business activities, not recurring. increase in value of asset, part of sales proceeds of an asset over and above the book value of an asset,

Income and gain are the net positive result of a financial operation/transaction.Normally , The term Income is used for professions/services. and profit or gain for business.

Revenue is the gross receipt of an operation like sales, turnover  for business ,profession ,services etc.,

Income has not been defined in accounting books, but in general dictionary meaning (in one of the dictionary) income is "The amount of money or its equivalent received during a period of time in exchange for labor or services, from the sale of goods or property, or as profit from financial investments."

Any type of gain which increase the wealth of a person is also income.