A short link between two devices close by. They pair once and remember each other, so when one refuses to connect the fix is usually to forget it and pair again.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a whisper that only carries across the room.
For example
Your headphones connect the moment you take them out of the case. They only do that within about the length of a room.
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.