Accretion refers to the process by which matter is accumulated or gathered together, often in the context of celestial bodies. In astronomy, it describes how dust and gas in space come together to form larger structures, such as stars and planets. This process is crucial for the formation of the universe as we know it, allowing for the creation of various celestial objects. In a more specific sense, accretion can also refer to the growth of black holes, where they draw in surrounding matter, increasing their mass over time. This phenomenon is essential for understanding the dynamics of galaxies and the evolution of the cosmos.