Cookie information

The cookie that sounds the most sinister to me is the one that says to “match and combine data from online and offline sources” and I think goes on with an equally vague “in support of one or more purposes”.

We are all very aware that cookies are there to attempt to track our every move online to learn everything about us but what is the offline tracking? It feels uncomfortably like ‘actual’ spies to go with the ‘virtual’ ones.

I have not found a satisfactory answer to this so I wonder if anyone has an idea or can direct me to a cookie explainer for dummies