What does approximation mean?
The definition of approximation
Ap*prox`i*ma”tion. n.
Etym: [Cf. F. approximation, LL. approximatio.]

1 The act of approximating; a drawing, advancing or being near; approach; also, the result of approximating. The largest capacity and the most noble dispositions are but an approximation to the proper standard and true symmetry of human nature. I. Taylor.
2 An approach to a correct estimate, calculation, or conception, or to a given quantity, quality, etc.
3 (Math.)

(a) A continual approach or coming nearer to a result; as, to solve an equation by approximation.
(b) A value that is nearly but not exactly correct.