The straight line drawn from the leading to trailing edges of the airfoil is called the chord line . The chord line cuts the airfoil into an upper surface and a lower surface. If we plot the points that lie halfway between the upper and lower surfaces, we obtain a curve called the mean camber line . But in most cases, these are two separate lines. The maximum distance between the upper and lower surfaces is called the thickness .
Airfoils can come with all kinds of combinations of camber and thickness distributions.