A receptor is a specialized protein molecule located on the surface of cells that recognizes and binds specific molecules in the body, such as hormones, neurotransmitters, or drugs. When a molecule binds to a receptor, it triggers a series of cellular responses that carry out various functions in the body. Receptors play a crucial role in communication between cells and are involved in processes such as signaling, gene expression, and immune response. Research in the field of receptors aims to understand their structure, function, and the mechanisms by which they regulate cellular activities, with implications for the development of new drugs and treatments for various diseases.