Define covalent bond in terms of electrons.
Two atoms can stick together to become a molecule. One method in which these atoms can stick together is by covalent bonding.
Covalent bonding occurs when the atoms are unstable. These atoms are unstable because their outer rings of electrons are not filled.
In order for the atoms to reach stability, electrons are shared between the unstable atoms, filling in the outer rings, and causing the atoms to become stable again.
Because of the process of sharing electrons that occurs during covalent bonding, it is sometimes referred to as shared bonding.