Renaturation of a protein is the opposite of the phenomenon of denaturation: when the medium containing a protein returns to its normal conditions (pH, temperature, etc.), the denatured protein returns to its initial conformation.
Under these conditions, the binding between the protein molecules is restored and all of the polypeptide chains return spontaneously to their three-dimensional structures (secondary and tertiary structures).
Renaturation of a protein allows it to return to its three-dimensional conformation. © PDB, Wikimedia public domain