Complex sentence: The informal sector is an economic sector that is neither taxed in any form however it is neither monitored by any form of government, and is not included in that government's Gross National Product (GNP), as opposed to a formal economy.
Split into simpler sentences: The informal sector is an economic sector that is not taxed in any form. It is neither monitored by any form of government, nor is it included in that government's Gross National Product (GNP), as opposed to a formal economy.