A system that allows an untrusted application to run in a highly controlled environment where the application’s permissions are restricted to an essential set of computer permissions. In particular, an application in a sandbox is usually restricted from accessing the file system or the network. A widely used example of applications running inside a sandbox is a Java applet.
Source(s):
NIST SP 800-95 from NIST ITL Bulletin, Mar. 2000

  A restricted, controlled execution environment that prevents potentially malicious software, such as mobile code, from accessing any system resources except those for which the software is authorized.
Source(s):
CNSSI 4009-2015 under sandboxing
NIST SP 800-179 under Sandboxing from NISTIR 7298 Rev. 2

  Isolating each guest OS from the others and restricting what resources they can access and what privileges they have.
Source(s):
NIST SP 800-125 under Sandboxing

  A restricted, controlled execution environment that prevents potentially malicious software, such as mobile code, from accessing any system resources except those for which the software is authorized (Under Sandboxing).
Source(s):
NIST SP 1800-21B from CNSSI 4009-2015