Those parts of the economy which operate through institutions which feed figures into official statistics. This includes firms organized as companies, payments made via the banking system, incomes reported to the tax authorities, sales reported to the VAT authorities, and employment reported to the National Insurance authorities. These constitute the vast majority of total economic activity in advanced economies. The organized sector is contrasted with the informal or hidden economy, in which individuals, voluntary bodies, and criminal organizations engage in trade, mainly for cash. Which is not reported to the tax authorities, and employment, also for cash. Which is not reported to the tax or social security authorities.
Reference: Oxford Press Dictonary of Economics, 5th edt.