In the field of chemistry and biochemistry, a ligand refers to a molecule or ion that is able to bind to a central metal atom or ion to form a coordination complex. Ligands can vary in size and complexity and can include molecules such as water, ammonia, or carbon monoxide, as well as larger organic molecules like amino acids or proteins. Understanding the interactions between ligands and metal ions is important in fields ranging from medicinal chemistry to materials science, as it can affect the properties and reactivity of the resulting complex. Studying ligand chemistry can help researchers design new drugs, catalysts, and materials with desired properties.