What is sieving? Where it is used?

Sieving - Sieving is a method in which fine particles are sieved through holes of the sieve while the bigger impurities remain on the sieve.

The Sieve has minute holes in it to allow the passage of small substance.

 Eg: Sieving is used in a flour mill to separate impurities like husk and stones from wheat before grinding it.