Elaborate

Author: Andy Hanson

pages/Modules.md

@@ -519,7 +519,10 @@ x(y);
 
 ### UMD modules
 
-Some libraries can be used either through imports or through globals.
+Some libraries are designed to be used in many module loaders, or with no module loading (global variables).
+These are known as [UMD](https://github.com/umdjs/umd) or [Isomorphic](http://isomorphic.net) modules.
+These libraries can be accessed through either an import or a global variable.
+For example:
 
 ##### math-lib.d.ts
 
@@ -536,7 +539,8 @@ isPrime(2);
 mathLib.isPrime(2); // ERROR: can't use the global definition from inside a module
 ```
 
-It can also be used as a global variable, but only inside of a script:
+It can also be used as a global variable, but only inside of a script.
+(A script is a file with no imports or exports.)
 
 ```ts
 mathLib.isPrime(2);