Clathrin is a protein that forms a complex lattice-like structure on the surface of cells, known as a clathrin-coated pit. It plays a crucial role in the process of endocytosis, whereby cells take up external molecules and particles. Synonyms for clathrin include clathrin heavy chain, clathrin light chain, and clathrin triskelion. Another related term is the AP-2 complex, which is a protein complex that interacts with and recruits clathrin to the membrane in preparation for endocytosis. The function and structure of clathrin and related proteins have been extensively studied due to their importance in various cellular processes, including synaptic vesicle recycling, membrane trafficking, and viral entry.