Definition of Octet Rule
The octet rule is the chemical rule of thumb that describes the phenomenon that the elements belonging to the main group form bonding with other atoms in such a way that each atom gets eight electrons in its outermost shell (valence shell). In this way, the atoms participating in the bonding have acquired stable electronic configuration as noble gases (Ne, Ar, etc.).
The octet rule is applicable to non-metals such as C, N, O, and halogens as well to metals like Na, Mg, etc. The atoms having less than eight electrons in their valence shell tend to react efficiently and form stable compounds.