What are coordination compounds?

(N/A) Coordination compounds are chemical compounds formed by the transition elements of the $d$-block of the periodic table.
When the $(n-1)d, ns$,and $np$ orbitals or $ns, np$,and $nd$ orbitals of a transition metal atom or ion are vacant,these elements accept electron pairs from anions or neutral molecules to form coordination compounds.
The bond formed between the metal atom/ion and the anions/neutral molecules in these compounds is known as a coordinate covalent bond.