Brownian motion is the random, erratic movement of microscopic particles suspended in a fluid (liquid or gas), resulting from their collision with the thermal motion of surrounding fluid molecules. As a fundamental concept in statistical physics and a key model for stochastic processes, it investigates the microscopic dynamics of particle-fluid interactions, characterized by unpredictable random walks and a mean-squared displacement proportional to time. Its significance lies in providing empirical evidence for the existence of atoms and molecules and serving as a foundational model for diffusion phenomena and general stochastic dynamics across diverse scientific fields.