Maybe something like referring to the value of a cell in a spreadsheet? So wikipedia could have a page on the number of users of web-app Foo, and that number would live update.

Sounds pretty useless.

Or maybe they're talking about the optimization hack in Python where some values of primitive types in Python only have one copy. If you don't know what I'm talking about, run this in a python console "import sys; sys.getrefcount(1)". You'll get the number of references to the number 1. Another fun trick: plot getrefcount for the first few thousands integers. It doesn't degrease monotonically as you might expect.