What is the difference between secondary and tertiary protein structure?

Secondary: localised folding within the polypeptide chain that is stabilised by hydrogen bonds. The most common secondary protein structures are alpha helices and beta sheets. Tertiary: this is the final form the protein takes once the different secondary structures have all folded into a 3D structure. This final shape forms and is held together through ionic interaction, disulphide bridges and van de Waals forces.