What are ligandssssss

In chemistry, I know that it has to do with covalent bonds but what is it? I need a definition please and one that makes sense too.
(P.S Sorry the question looks weird I needed 20 characters to submit)

A ligand is either an ion or molecule that bonds to central atom to form a complex ion.


A ligand differs from normal covalent bonding as it shares more than one electron, involved in the bonding. (electron pairs)

Any chemical substituent that bonds to a central atom or has an affinity to bond to a molecule. In cuprictetraammine(II), copper is the central atom and the four ammonia molecules that are covalently bonded to the copper ion are the ligands.

Another example is hemoglobin, the allosteric protein that binds oxygen. Oxygen has an affinity to covalently bond to the ferrous ion bound to the prosthetic group in a single hemoglobin subunit. The oxygen is therefore a ligand to the hemoglobin molecule because it has a tendency (or affinity) to bind to hemoglobin.