On the cover of the box there are a number of terms and symbols which are important to understand when making an order or when comparing prices. The symbols you will find on most lens packaging are:
Sf, Sph or sphere which indicates the strength of the lenses; should you be shortsighted the symbol will display a minus sign before the number: whereas a plus sign will be displayed should you be longsighted.
BC means base curve and indicates how rounded the lense is. It usually lies somewhere between 8.0 and 9.0 degrees on soft lenses.
Dia indicates the diameter of the lense size the whole way across. That measurement more often than not lies between 13.8 and 14.5 degrees on soft lenses.
Lenses correcting astigmatism additionally bare two other symbols:
Cyl or Cylinder which provide the degree of correction the lenses provide against astigmatism.
Ax or Axis displays at what degree the lens corrects astigmatism on a scale spanning from 0 degrees to 180.