Winterfylleth was the Anglo-Saxon or Old English name for the month of October. It marked and celebrated the beginning of winter.
The name of the month was recorded by the Venerable Bede thus:
Antiqui Anglorum populi […] annum totum in duo tempora, hiemis et aestatis dispertiebant, sex menses […] aestati tribuendo, sex reliquos hiemi; unde et mensem, quo hiemalia tempora incipiebant, Wintirfylliþ appellabant, composite nomine ab hieme et plenilunio, quia videlicet a plenilunio ejusdem mensis hiems sortiretur initium […] Wintirfylliþ potest dici compositio novo nomine hiemi pleniuni.
The old English people split the year into two seasons, summer and winter, placing six months — during which the days are longer than the nights — in summer, and the other six in winter. They called the month when the winter season began Wintirfylliþ, a word composed of "winter" and "full moon", because winter began on the first full moon of that month.
Though in modern times in this month, Halloween is celebrated in America, England and elsewhere, it is not linked to Old English tradition, though many of the customs are English in origin.
^Bosworth, Joseph. "An Anglo-Saxon Dictionary Online." Winter-fylleþ. Ed. Thomas Northcote Toller and Others. Comp. Sean Christ and Ondřej Tichý. Faculty of Arts, Charles University in Prague, 21 March 2010. Web. 20 September 2014. <http://bosworth.ff.cuni.cz/035945>.