RE: Airfoil Numbers
Just like Lomcevak Duck said, naming and numbering are just a way to separate different airfoils. The system used in naming these depends entirely on the designer. However, there are a few families that have meaning behind the naming. Your example of a NACA (which was the government agency before the current NASA) 4-digit airfoil is one of these families. The first number described the maximum camber in a percent of the chord length, the second number indicated the location of the maximum camber in terms of the chord length and the final number was the maximum thickness. So, if we had a NACA 4412 airfoil, it would mean that it had a 4% maximum camber located at 40% down the chord length and 12% maximum thickness. NACA produced hundreds of airfoils based on this system and then expaned to a 5-digit (NACA 23015), 6-digit and lesser known 7-digit systems. A good book to learn all about this is "Theory of Wing Sections" by Abbot.
Newer families of airfoils have the location of boundary layer transistion and all kinds of neat stuff encoded into the number of the airfoil.