Cosmic chronometers are a class of observational constraints used in cosmology to measure the age and expansion rate of the universe. This method relies on the measurement of the ages of old and passively evolving galaxies, which can serve as "cosmic clocks" to provide information on the rate at which the universe has been expanding over time. By studying these cosmic chronometers, researchers can gain insight into the history and evolution of the universe, as well as test different cosmological models. This area of research is crucial for understanding the fundamental properties of the universe and its origins.