Popular etymology often links Fastnacht (in Mainz also Fassenacht, in Switzerland Fasnacht, in Swabia Fasnet, Fasent) with fasten ("to fast") – allegedly from celebrations on the eve preceding fasting. In the beginning of the 20th century it was a common assumption that the tradition has its root in the pre Christian rituals. So there was an assumption Comparison of dialect variants however yields an OHG *fasanaht, with an element fasa- of unclear meaning. A likely derivation looks to PIE pwo- "purify" (cognate to pava-mana), or alternatively to Middle High German vaselen "prosper, bud", and interprets the festival as a fertility rite. But historians around Werner Mezger refuted all those theories, and showed that the name came from fasten ("to fast") and the tradition is Christian. They also showed that a lot of the ritus came from the civitas diaboli model of the Catholic church.
Fasching (MHG vaschanc or vaschang) is related, probably originally with a second element -gang instead of -nacht.
Fastnacht is held in the settlement area of the Germanic tribes of the Swabians and Alemanns, where Swabian-Alemannic dialects are spoken. The region covers German Switzerland, the larger part of Baden-Württemberg, Alsace, south-western Bavaria and Vorarlberg (western Austria).
The festival starts on the Thursday before Ash Wednesday, known as Schmotziger Donnerstag. In Standard German, schmutzig means "dirty", but in the Alemannic dialects schmotzig means "lard" (Schmalz), or "fat"; "Greasy Thursday", as remaining winter stores of lard and butter used to be consumed at that time, before the fasting began. Elsewhere the day is called "Women's Carnival" (Weiberfastnacht), being the day when tradition says that women take control. In particular regions of Tyrol, Salzburg and Bavaria traditional processions of the Perchten welcome the springtime. The Schönperchten (beautiful Perchts) represent the birth of new life in the awakening nature, the Schiachperchten ("ugly Perchts") represent the dark spirits of wintertime. Farmers yearn for warmer weather and the Perchtenlauf (Run of Perchts) is a magical expression of that desire. The nights between winter and spring, when evil ghosts are supposed to go around, are also called Rauhnächte (rough nights).
Swabian-Alemannic Fastnacht distinguishes itself from the Rhenish Carnival but did not develop an independent form until the first quarter of the 20th century. Whilst Carnival developed a new form of Fastnacht in the 18th century, an influence, which was taken up by the Swabian-Alemannic Fastnacht as well, contemplations to look back took place in the 20th century, recalling the traditions of Fastnacht in the Middle Age and the Early modern period.