What is meant by a cosmic horizon?

A cosmic horizon refers to the boundary of the observable universe, beyond which light has not had enough time to reach us since the Big Bang due to the finite speed of light and the expansion of the universe. This horizon delineates the limit of what we can see, meaning that regions beyond it are fundamentally inaccessible and remain unknown. The cosmic horizon is dynamic; as the universe expands, the observable universe grows, allowing us to see more over time.