Accessing page variables

We're trying to set up a glossary of terms, with buttons on the pages where the terms show up, that when clicked, take you to the glossary page and display the definition.

Seems simple enough:

Set up a variable on the glossary page, when the page loads, check the variable and display information dependent on its value.

Then create buttons over the terms, that when clicked, set that variable, and change the page.

Issue:

The buttons cannot see or modify that variable.

What now?