OD = right eye
OS = left eye
OU = both eyes (in this case, fill in the same information for both the OD and OS fields)
Power (PWR) or Sphere (SPH) = main power of the lens, in diopters. Take careful note of the sign (+) or (-) preceding the number.
Cylinder (CYL) = astigmatism power, if your Rx has any, in diopters. Take careful note of the sign (+) or (_) preceding the number.
Axis (AXIS or X) = orientation of the Cylinder power, in degrees. If the Rx from your doctor isn't written on a pre-preinted grid, there is typically a letter "x" written before it (i.i. x080 is shorthand for Cylinder power axis is at 80 degress).
Add (ADD) = how strong the bifocal portion of your lens is, if your Rx has any, in diopters.
Base Curve (BR or BCR) = radius of curvature of your contact lens; it's a measurement in mm of how cupped or how flat the lens is. The lower the number, the more cupped the lens; the higher the number , the flatter the lens is.
Diameter (DIA or OAD) = overall diameter of the lens, in mm.