Sandbox: is a security mechanism for separating running programs. It is often used to execute untested code, or untrusted programs from unverified third-parties, suppliers and untrusted users. (Wikipedia)
Ok, lets cut it simple. Sandbox is a software which you use to open other programs, These programs which we open are suspicious(untrusted) programs so that even if they are any Virus, Keylogger or R.A.T they would not be installed on your computer and your computer will not be effected by it. So if you are encountered by any software about which you are not sure that it is clean you should be open it with Sandbox.
One example of Sandbox is Sandboxie which you can download from here : http://www.sandboxie.com/index.php?DownloadSandboxie
