It is a form of chemical bonding whereby atoms of elements share electrons so as to attain a stable state. Here, the two atoms involved, contribute equally electrons to be shared e.g. In O2, Cl2, Hcl, NH3 etc.
However, when one of the participating atoms contributes the pair of electrons to be shared by the two atoms, it is termed dative or coordinate covalent bonding.
e.g. (1) In the formation of H30
(2) In the formation of NH4