Context is the object that is the target of a menu command.
Usually the context is the current selection or the item under the mouse when invoking a context menu.
// Add context menu named "Do Something" to context menu
@MenuItem ("CONTEXT/Rigidbody/Do Something")
static function DoSomething (command : MenuCommand) {
var body : Rigidbody = command.context;
body.mass = 5;
}