A 737 is a medium-sized passenger plane made by Boeing, a big US company. Airlines use it for trips that are not the longest in the world — a few hours, many cities, many flights a day. If you have flown in East Asia, there is a fair chance you have sat in one; you just may not have read the number on the outside.

There is not one single 737. Boeing has built many versions for fifty-plus years, with different engines, different lengths, and different computer systems. News about a 737 crash or a grounded fleet is usually about one version, not every 737 in the sky. Still, in ordinary talk “a 737” just means that familiar narrow Boeing jet.

People around planes often say “seven thirty-seven” or “seven three seven.” It is a model name, as ordinary as a car’s name, not posh and not slang.