What is meant by the different sectors of economies?

Economies are made up of three sectors; the primary sector, which involves extraction of raw materials (e.g. timber), the secondary sector, which is concerned with manufacturing (e.g. turning timber into chairs), and the tertiary sector, which provides services to people (e.g. a haircut). The relative sizes of these sectors often reflect the economy's development level; economies of developed countries such as the UK have a large tertiary sector, a declining secondary sector, and a small primary sector, whereas developing countries often have a large secondary sector, and less developed countries may have a large primary sector.