blue box

noun4

1. •
   (UK, Canada) A blue container used for the collection of household waste (such as tin cans and newspapers) for recycling by a municipal authority.
2. •
   (historical) An electronic device used to bypass payment on a tone pulse telephone system.
3. •
   (US) Ellipsis of USPS blue box.
4. •
   (US, informal) A "tornado watch" notification category.