SdB stars, also known as subdwarf B stars, are a type of hot, compact stars that are located on the extreme horizontal branch of the Hertzsprung-Russell diagram. These stars are thought to be the stripped cores of red giant stars that have lost most of their outer envelope. SdB stars are characterized by their high surface temperatures (around 20,000 to 40,000 K) and low luminosities, which are typically less than 1% of the Sun's luminosity. They are also known for their strong helium lines in their spectrum. Research on SdB stars often focuses on understanding their formation and evolutionary history, as well as their impact on stellar populations and galactic chemical evolution. These stars are also of interest to astronomers studying stellar pulsations, asteroseismology, and variable stars. Overall, SdB stars provide valuable insights into the late stages of stellar evolution and the properties of compact, hot stars.