Transit spectroscopy is a technique used in astronomy to study the atmospheres of exoplanets by measuring the changes in a star's light as a planet passes in front of it, or transits. This method allows scientists to analyze the composition and properties of exoplanet atmospheres by studying the absorption or emission lines in the star's spectrum during the transit. Transit spectroscopy has been used to detect various elements, molecules, and compounds in exoplanet atmospheres, providing valuable insights into their composition and potential habitability.