Its just a retaining circlip,
multiple uses, accross many factors, not a bike specific item.
They are normally pretty robust, and need quite a bit of force to remove,
they dont normally fall off through wear though. , or get levered off by the part there fitted to wearing / moving and forcing the clip off
usually not fitted properly and the ping off after time.
Nothing to do with brake rotors afaik.
pad retaining pins are R clips, and the rotors are bolted / screwed in