Letter-size names a sheet of paper: 8½ inches wide and 11 inches long (about 216 × 279 mm). It is the everyday printer paper in the United States — the size people there mean when they say “a letter” as stationery. Taiwan, and most of the world, uses A4 instead. A4 is a little narrower and a little longer. If you print a US letter-size file on A4, the edges may clip or the margins look wrong; the other way around, you get extra space. You will see letter-size on American printers, in office software (often the default when the program is set to US), and on envelopes and folders sold for that market. It is a practical office word, not a poetic one. Legal-size is the longer American cousin (8½ × 14 inches).