Google Sandbox is a filter to prevent the new Google sites to take the top positions in search results, but Google has a total ban on the inclusion of web search results. According to the sandbox effect, links which may normally be weighted by Google's ranking algorithm, not least improving the position of a web page in Google's index, may be subjected to filtering to prevent their having a full impact.

Google SandBox = Old phrase/term.
It referred to sites that were "restricted" in some ways in performance, limiting their ability to do well i nteh SERPs for certain/all search terms etc.

It is Now a commonly mis-used term, as the SandBox effect that is referred to kind of disappeared sometime ago.

there is no official statement from Google that such a thing exists.

Sandbox effect means links weighted normally by Google's ranking algorithm but not improving position of web-page in its index.

Google sandbox is one in which website gradually losses their ranking at a definite period of time. In the mean time google checks that contain backlinks from ethical way or not.