The informal sector, informal economy, or grey economy is the part of an economy that is neither taxed, nor monitored by any form of government. Unlike the formal economy, activities that are engaged in the informal economy are not included in the gross national product (GNP) and gross domestic product (GDP) of a country. The informal sector can be described as a grey market in labour.Other concepts which can be characterized as informal sector can include the black market(shadow economy, underground economy), the agorism, and System D. Associated idioms include ""under the table"", ""off the books"" and ""working for cash"".Although the informal sector makes up a significant portion of the economies in developing countries – about 41% in 2000 according to the official GNI metric – it is often stigmatized as troublesome and unmanageable. However the informal sector provides critical economy opportunities for the poor and has been expanding rapidly since the 1960s. As such, integrating the informal economy into the formal sector is an important policy challenge.