Cosmological constraints refer to the limits or boundaries that cosmologists and astrophysicists are able to place on various parameters and theories within the field of cosmology. These constraints are derived from observational data gathered from telescopes, satellites, and other instruments, as well as theoretical models and simulations. By analyzing the cosmic microwave background radiation, the distribution of galaxies, the abundance of elements in the universe, and other phenomena, scientists are able to place constraints on key cosmological parameters such as the rate of expansion of the universe (the Hubble constant), the density of dark matter and dark energy, and the age and size of the universe. These constraints help to test and refine cosmological models, improve our understanding of the universe's origins and evolution, and provide insights into fundamental questions about the nature of matter, energy, and the universe as a whole.