The viewport of every device you are asked to support, in the CSS pixels a media query actually reads, with the Tailwind breakpoint each one lands in.
Because 1179 is hardware pixels. CSS sees 393 at a device pixel ratio of 3, and 393 is the number your breakpoints are compared against.
Design for the ranges between them. A layout pinned to one phone breaks on the next; the list is here to tell you where the crowds are, not to be a set of targets.
Which Tailwind breakpoint that width satisfies. An iPad at 820 is md but not lg, which is exactly the case people forget to check.