What is the tertiary sector? How is it related to the primary, secondary and tertiary sectors?

The fourth sector is an extension of the Clark Classification (primary sector: agriculture, secondary sector: industry, tertiary sector: all other sectors except the primary and secondary sectors), which refers to the public **** industry that has no obvious profit for itself but can improve the profit of other sectors.

The main forms of the fourth industry are: simple services and technical services, including medical care, maintenance, decoration, beauty salon, cabaret, sports and other direct use of natural resources, industrial products, intellectual products, combined with the use of man's own biological and physical resources (including the human body, physical strength and skills) to provide services to meet the human being (or the human being's biological property, such as pets) their own physiological, physical, psychological, and other needs.