" is an attack technique used to exploit web sites by executing Operating System commands through manipulation of application input.
When a web application does not properly sanitize user-supplied input before using it within application code, it may be possible to trick the application into executing Operating System commands. The executed commands will run with the same permissions of the component that executed the command (e.g. Database server, Web application server, Web server, etc.)." -Web Application Security Consortium Threat Classification