Malcom-

>I've seen this phrase used a few times. Can someone explain what it means?

Do you mean "wrapper?"

If so, than it is pretty much what it sounds like...it is a program or a class that wraps itself around existing code in order to provide a streamlined way to access the old code.

For example, if you have some legacy procedural code that is difficult to understand, it may not be worthwhile rewriting it in a object oriented manner, but you can wrap a class around it that has some methods and properties that clients of the class access in order to use the code.

I think of wrappers as isolation code. They isolate some other code or objects, simplifying access to something more complex.

This is how I understand the concept and isn't an "official" definition.