Several files squeezed into one, which has to be unpacked before use. It is also a favorite wrapper for malware, because the contents stay hidden until you open it.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a vacuum bag for clothes.
For example
Twenty photographs arrive as one file. Nothing opens until you unpack it, and then all twenty are there.
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.