One quarter
On Windows, hold Alt and type 0188 or 172 on the number pad, then let go of Alt.
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About the one quarter
A quarter is one of only three fractions, with ½ and ¾, that Latin-1 offered as single characters, so it has long been simple to type. Unicode files it as a vulgar fraction, an old term from the Latin vulgaris, common, for a fraction made of whole numbers.