A stock market sector is a collection of stocks that have a lot in common, typically because they are in similar industries. According to the most widely used classification system, the Global Industry Classification Standard, there are 11 different stock market sectors (GICS).
The order of the 11 sectors based on size is as follows: Information Technology, Health Care, Financials, Consumer Discretionary, Communication Services, Industrials, Consumer Staples, Energy, Utilities, Real Estate, and Materials.

The stock market encompasses various sectors that represent different segments of the economy, each comprising companies with similar business activities. Commonly, these sectors are grouped into 11 categories, known as the Global Industry Classification Standard (GICS):

1. Information Technology: Companies involved in technology and software development.
2. Health Care: Encompasses pharmaceuticals, biotechnology, and health services.
3. Financials: Includes banks, insurance, and other financial institutions.
4. Consumer Discretionary: Involves non-essential consumer goods and services.
5. Communication Services: Companies providing communication-related services.
6. Consumer Staples: Encompasses essential consumer goods like food and household products.
7. Utilities: Includes companies providing essential services like water and electricity.
8. Energy: Involves companies related to oil, gas, and energy exploration.
9. Industrials: Encompasses manufacturing, construction, and industrial services.
10. Materials: Includes companies involved in raw materials and commodity production.
11. Real Estate: Involves companies in property development and management.

Investors diversify their portfolios across these sectors to manage risk and capitalize on varied market opportunities. Each sector reacts differently to economic conditions, contributing to the overall stability and growth of a well-balanced investment portfolio.