French Wire
A fine coil of wire threaded over the silk at each end of a strand, protecting the thread where it turns at the clasp.
The thread takes all its wear at the two points where it loops through the clasp. French wire sleeves that loop in a flexible metal coil.
Without it the silk rubs against the clasp ring and eventually parts, which is how most strands break.
It is a small detail that separates properly finished stringing from quick work.
When you are buying
Look at the last centimetre before the clasp. A neat metal coil there tells you the piece was strung by someone who expected it to last.
Stringing
The thread a strand is built on, and the craft of assembling it.
Knotting
A knot tied between each pearl on the thread. It stops pearls rubbing and limits a break to a single lost pearl.
Restringing
Replacing the thread a strand is built on. Routine maintenance, not repair, and overdue on most pearl necklaces.
Clasp
The fastening that closes a necklace or bracelet. The most common point of failure and the most overlooked part of a purchase.