Receptor-mediated endocytosis is a cellular process where cells absorb molecules by using specific receptors on their surface. When a target molecule, such as a hormone or nutrient, binds to its corresponding receptor, the cell membrane invaginates, forming a pocket that eventually pinches off to create a vesicle containing the molecule. This method allows cells to take in essential substances efficiently and selectively. It plays a crucial role in various biological functions, including the uptake of cholesterol, iron, and certain viruses. By using receptors, cells can regulate their internal environment and respond to changes in their surroundings.