The trail you leave, assembled from many small traces rather than one big one. Deleting a post rarely removes it — copies and records usually outlive the original.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
footprints in wet cement, not sand.
For example
You delete an old post. A screenshot of it is still on somebody else's phone, and the search engine remembers it for another month.
This is one card out of 275.
The hundred words you meet most are free — the whole set, animated, in one file that works with no internet.
Volume 1 has all 275 in fifteen chapters, with Staying Safe the largest chapter on purpose.