I'm a physicist trying to learn some chemistry for my research (on-surface reactions and assembly) but am having some trouble with getting the meaning of some of the terms straight. Often one source seems to contradict another, in my reading of it at least. Specifically, the meaning of the term Ligand. My understanding is that it is a non-metallic group at has formed a coordinate bond to a metal centre by donating a pair of electrons. This is what forms a complex. However, I have seen the term applied to groups added to a metal through oxidative addition. My understanding is that this process forms a direct covalent bond (not a coordinate bond) to the metal as the metal loses its electrons (is oxidized) rather than has some donated to it. Is my understanding of this reaction incorrect or is the term ligand used more widely to describe any group bonded to a metal in any way?