alt Hacker News+1 for frankfurter and wiener, because those are regional synonyms for basically the same type of sausage. of course it might have some local adjustments, but you know what to expect. https://en.wikipedia.org/wiki/Vienna_sausage
but brat? a Bratwurst is a very different kind of sausage. thicker, different meat, different taste, different preparation, different taste. frankfurter / wienerli, are commonly boiled in water, bratwurst go on a grill. (Brat = braten = roast).
i got a western-european POV. maybe USians use these words differently. which means they're wrong. or wronger than europeans are when arguing what stuff should be called. doughnut / berliner / krapfen / [insert name you use], just to trigger some people.
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Bratwurst and wieners are indeed different sausages in the US, but funnily enough you would never boil a wiener here, they are always grilled or microwaved in a pinch. Whereas brats are somewhat commonly boiled (often in beer) to cook the inside, then finished on the grill to brown the outside. Though I personally cook them entirely on the grill, as I think the boiling method is somewhat cheating.
In Germany Frankfurter are pork only and Wiener are pork and beef