A vesicle is a small, membrane-bound sac within a cell that serves various functions, including transporting materials, storing substances, and facilitating biochemical reactions. Vesicles can contain different types of molecules, such as proteins, lipids, or waste products. They play a crucial role in processes like endocytosis, exocytosis, and intracellular transport. In addition to their cellular functions, vesicles are also involved in signaling pathways and maintaining cellular homeostasis.