1. <operating system> A protected, limited environment where applications (e.g. Java programs downloaded from the Internet) are allowed to "play" without risking damage to the rest of the system.
2. <jargon> A term for the R&D department at many software and computer companies (where hackers in commercial environments are likely to be found). The term is half-derisive, but reflects the truth that research is a form of creative play.
3. <operating system> link farm.