The chip that tells the network which number is yours. It can be moved to another phone, which is exactly what SIM-swap fraud does to intercept the codes sent to you.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
your membership card to the phone network.
For example
You buy a new phone. The shop moves a tiny card from the old one into the new one, and your number comes with it.
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.