There is no definition for black money in economics. Different people define it in different terms such as unaccounted income, underground income, black wealth, or at economy level it is known as parallel economy, black economy, shadow economy and unofficial economy.
There are certain sectors and activities like land and real estate transactions, bullion and jeweller dealings, complex financial market transactions, charitable activities, informal sector and cash economy, self-employed professionals, external trade and transfer pricing, forms the origin to the culmination of black money.
Broadly or in layman's language we can define it as, money that has been acquired through illegitimate means or money which is unaccounted for, that is, for which tax is not paid to the government. Black money may be generated either by illegitimately drug trade, terrorism, corruption, or legitimate failure to pay the dues to the public exchequer yielding the generation of unaccounted wealth.
Black money causes financial leakage, as unreported income that is not taxed causes the government to lose revenue. In addition, these funds rarely enter the banking system. As a result, it can be more difficult for legitimate small businesses and entrepreneurs to obtain loans.
Black money may be generated through the crude approach of not declaring the income or the activities leading to it. This is the likely approach in all cases of criminal, illegal, and impermissible activities. Another approach can be by not declaring or reporting activities and the income generated there from may also be followed in cases of failure to comply with regulatory obligations or tax evasion on income from legitimate activities.
However, complete evasion or non-compliance may make such incomes vulnerable to detection by authorities and lead to consequent adverse outcomes for the generator. Thus, a more sophisticated approach for generation of this kind of black money is often preferred, involving manipulation of financial records and accounting.
Tax evasion involves misreporting or non-reporting of the transactions in the books of account.