Airfoils can be classified as either symmetrical or asymmetrical, based on the camber.
Symmetrical airfoils are called so since their upper and lower surfaces are the same and hence have zero camber. Asymmetrical airfoils have a non-zero camber, meaning their upper and lower surfaces are different.
Traditionally, symmetric airfoils have been widely used, but in the past few decades, aircraft manufacturers have been shifting to asymmetrical airfoils for their better lift and handling capabilities. However, symmetrical airfoils continue to be used till date, especially in aerobatic aircraft.
Shown above is the NACA0012, a popular symmetrical airfoil. It was used in the rotor of the Bell 205 UH-1 helicopter.
Shown above is the NACA4412, another popular asymmetrical airfoil. It was used as the outboard wing airfoil in a variety of aircraft including the Avtech Jabiru and the Aeronca 65- TAC Defender.