The following words may be used as keywords in future evolutions of the language, so using them as identifiers should be avoided to allow an easier adoption of those potential future evolutions:
The following code snippet illustrates this rule :
var package = document.getElementsByName("foo"); // Non-Compliant var elements = document.getElementsByName("foo"); // Compliant var data = { package: true }; // Compliant, as it is not used as an identifier here