X-Plane uses Airfoil Files, designated by the file suffix .afl, to determine the aerodynamic performance of a given wing cross-section as it moves through the air. AFL files are created using the AirfoilMaker application, and describe the lift, drag and pitching moment of an airfoil over a range of Angles-of-Attack.
Some basic characteristics of an airfoil can actually be discerned from most common airfoil names. For example, in the 4-digit NACA airfoil series, for an airfoil such as NACA 2412, the first two digits tell something about the airfoil shape and how much lift it may generate at 0 degrees AOA, while the last two digits tell the thickness ratio of the airfoil, in this case 12%. Likewise, NACA 0009 tells you that it is a symmetrical airfoil with a thickness ratio of 9%.
For more information on NACA airfoil naming conventions, see This Link at Aerospaceweb.org