Open a kitchen drawer and most of what is in it is stainless steel: the spoons, the whisk, the good pan, the sink it all gets washed in. Look at a product listing, or sometimes the bottom of a bottle, and the same numbers keep showing up: 304, and 316 or 316L. They are the grades most everyday steel things are made from.
304 is the one you live with. It takes boiling water, lemon juice, the dishwasher and years of being dropped into a sink, and comes out looking much as it went in. The chromium in it covers the metal in a film too thin to see, and when you scratch it, the film grows back.
316 is the same steel with a little molybdenum added, and that lets it stand up to salt. It goes on boats and into things that live near the sea. 316L is its low-carbon version, made for parts that get welded.
It started with a gun barrel. In 1913 Harry Brearley, a metallurgist in Sheffield, was looking for a steel that would wear less when fired through, and found one that shrugged off rust. Within a couple of years, Sheffield cutlers were selling knives that stayed bright after dinner.
The trade-off is weight. A steel bottle feels solid in the hand and heavy by the end of a day in a bag, and both grades carry some nickel, which a few people are sensitive to. For the things that stay at home, the pot, the kettle, the spoon, the weight hardly matters. For the things that travel with you, it starts to.