what reference of airfoil is used to define lift and drag?
This is a basic question, and I give you the answer from the initial pages of a aerodynamic learning textbook.

The  is presented in next figure:



Where:


L: lift: component of R (resultant force) perpendicular to air stream,
D: drag: component of R parallel with the air stream,
N: Normal Force: component of R perpendicular to chord,
A: Axial Force: component of R parallel with chord,


For further information you can refer to Anderson's Aerodynamic book.