In the middle of October 2018, Google Tag Manager silently introduced a new feature that caused some questions in the GTM community (including me), an Undefined variable.
In this quick guide, I’ll shed some light on what an Undefined variable in Google Tag Manager is and where you can use it.
First of all, you can find this variable among other User-defined variables in your GTM container:
It is simple to configure. In fact, it has no settings at all