In statistics, see estimation theory, estimator.
In mathematics, approximation or estimation typically means finding upper or lower bounds of a quantity that cannot readily be computed precisely and is also an educated guess . While initial results may be unusably uncertain, recursive input from output, can purify results to be approximately accurate, certain, complete and noise-free.
In project management, see estimation (project management).
Construction Estimating- www.aspenational.org
Estimation!