In general, a sector refers to a specific segment of the economy in which businesses share the same or related business activity, product, or service. There are different types of sectors, including:

• Economic Sectors: One classical breakdown of economic activity distinguishes three sectors: primary, secondary, and tertiary. Primary involves the retrieval and production of raw-material commodities, such as corn, coal, wood, or iron. Secondary involves the transformation of raw or intermediate materials into goods, such as steel into cars or textiles into clothing. Tertiary includes services such as retail, arts, entertainment, and recreation, financial, transportation, and communications.

• Investment Sectors: In the financial markets, economic sectors are broken down even further into sub-sectors called investment sectors. Investment sectors represent a grouping of companies with similar business activities, such as technology, energy, and financial services.

• Circle Sectors: In geometry, a sector of a circle is a portion or part of a circle that is composed of an arc and its two radii. It is formed when two radii of the circle meet at both ends of the arc.

It is important to understand sectors because they can help investors classify companies that compete against each other and understand how a company is performing compared to its competitors.