A de Sitter universe is a model of the universe that describes a space with a positive cosmological constant, leading to an accelerated expansion. This concept is named after the Dutch mathematician and physicist Willem de Sitter, who first proposed it in the early 20th century. In this model, the universe is empty of matter but filled with dark energy, which drives the expansion. In a de Sitter universe, the geometry of space is curved, and it can be visualized as a hyperbolic space. This model helps scientists understand the large-scale structure of the universe and is relevant in cosmology, particularly in relation to the Big Bang and the current accelerated expansion observed in the observable universe.