Industry refers to economic activities connected with the conversion of resources into useful goods. It generally involves mechanical appliances and technical skills for activities relating to producing or processing goods, as well as breeding animals. The term is also used for groups of firms producing similar goods, such as the cotton textile industry or electronic industry.

Industries are divided into three broad categories: primary, secondary, and tertiary. Primary industries deal with the extraction and reproduction of natural resources. They include extractive industries, which draw products from natural sources like mining and farming, and genetic industries, which breed plants and animals, such as poultry farms and fish hatcheries.

Secondary industries transform resources into finished goods. They include manufacturing industries, which are further classified as Analytical (separating elements, e.g., oil refinery), Synthetical (combining ingredients, e.g., cement), Processing (successive stages, e.g., sugar), and Assembling (assembling parts, e.g., cars). Construction industries are also secondary, involved in building dams, bridges, and roads.

Tertiary industries provide support services to primary and secondary industries and assist trade. Examples include transport, banking, insurance, warehousing, and communication.