Some tangible examples are: credit card transaction data, individual geolocation or foot-traffic data from mobile phone sdks or carriers themselves, receipts scraped/exfiltrated from email inboxes, individual browsing history, or highly targeted web scraped data.

All "anonymized" of course.

"What Is Alternative Data and Why Is It Changing Finance?"

https://builtin.com/fintech/alternative-data

TL;DR: Info gleaned from just about any source other than company statements and market data, used to guide investment choices. This includes stuff like satellite imagery, which has been used for a long time for these sorts of purposes, but also e.g. social media trends. I guess the news is that there's more of it happening now, because the practice itself isn't new.

Fascinating.