My friend came home from the temple with a piece of ordinary white string which she tied on my wrist, what's it mean please?

Good luck... Not on getting an answer, that IS the answer I'm told..

She just 'tied the knot' with you..! It's usually just a sign of friendship, and good luck, but it is usually tied on by the monk himself. When you get married you can end up with dozens of them on your wrist..! I wear a dark red one, which came from a temple in the north. You should never untie them though, but cut them off with scissors, or a knife. :jap: