localism not found in any modern Chinese dictionaries, famous for its complexity. It is written with 57 strokes, and pity the poor sign-maker that has to paint it twice. No one knows for certain where the name originated, but the most plausible guess is that it represents the sound of the noodles being slapped against the work surface when being made. This theory is advanced by Xi'an Famous Foods' Jason Wang in this video. Biang Biang noodles, being "as wide and thick as belts" are also famous for that reason as one of the "ten strange wonders of Shaanxi." But don't look for "Biang Biang" noodles on your menu; although phonetic substitutes like 棒棒麵 (bàng bàng miàn) or 梆梆麵 (bāng bāng miàn) may sometimes be used, according to Wikipedia, the dish is most commonly listed on menus outside of Shaanxi as you po che mian (油泼扯面).
You po che mian, roughly "oil-sprinkled torn noodles" are wide wheat noodles tossed (or stirred) with chili oil and some or all of: bean sprouts, crushed garlic, chili flakes, cabbage, and cilantro. The noodles are made by tearing wide strips of noodle dough in two lengthwise, rather than iteratively pulling them to thinness as done with "hand pulled" noodles (la mian). Traditionally they were supposedly made more than an inch thick and a meter in length, but fortunately are found in a more manageable size nowadays. Biang biang mian/you po che mian is an excellent hot weather dish, hard to find even in China outside of Xi'an. If you're lucky enough to be in New York, though, head for the nearest outlet of Xi'an Famous Foods for the excellent version depicted in the photo at the top of this page.