Google sandbox refers to the commonly held belief or imaginary space where search engines stores the new websites as well as those websites which was affected due to changes in alorithms for a temporay period of time.
Google sandbox is an age filtering algorithm by Google in order to filter the over optimized site and spam sites. Every new site will spend some time a minimum of 3 months in getting ranked in search engines. This is mainly to reduce the spammers raising quickly in search engines.
The Google Sandbox Effect is a theory used to explain why newly-registered domains or domains with frequent ownership changes rank poorly in Google Search Engine Results Pages (SERPS). In other words new websites are put into a “sandbox” or a holding area and have their search ratings on hold until they can prove worthy of ranking.