An antibody is a protein produced by the immune system to identify and neutralize foreign objects like bacteria and viruses. They are specific to particular antigens, which are substances that trigger an immune response. When an antibody binds to an antigen, it can mark it for destruction or prevent it from entering cells. Antibodies are crucial for the body's defense against infections. They are also used in medical diagnostics and treatments, such as in vaccines and therapies for diseases like COVID-19. Understanding antibodies helps scientists develop better ways to protect and treat illnesses.