What defines the boundary for counting clusters in the observable universe inquiry?

The spherical volume from which light has had time to reach Earth

An accurate census of all clusters in the entirety of the cosmos is impossible due to the finite speed of light and the universe's age. Therefore, astronomical inquiry focuses strictly on the observable universe. This observable universe is defined as the specific spherical region centered on Earth from which light emitted by objects has managed to travel across space and reach us within the time elapsed since the Big Bang. Counting cluster prevalence relies on sampling the density within this known, measurable volume and then extrapolating that density figure across the total known volume enclosed by this cosmic horizon.