The cosmological constant, denoted by the Greek letter Lambda (Λ), was introduced by Albert Einstein in his equations of General Relativity to allow for a static universe, but it is now understood as a measure of the energy density of empty space, or dark energy, that is driving the accelerated expansion of the universe. This constant plays a crucial role in the current Lambda Cold Dark Matter (ΛCDM) model, which is the standard model of Big Bang cosmology.