What is the overlapping of atomic orbitals? When is a covalent bond formed?

(N/A) The overlapping of atomic orbitals is the partial interpenetration of atomic orbitals of two atoms when they come close to each other to achieve a state of minimum energy.
$A$ covalent bond is formed between two atoms by the pairing of electrons present in the valence shells that have opposite spins.
The extent of this overlap determines the strength of the covalent bond; greater the overlap,the stronger is the bond.