A Mare (Old English: mære, Old Dutch: mare; mara in Old High German, Old Norse and Old Church Slavic) is an evil spirit or goblin in Germanic and Slavic folklore which rides on people's chests while they sleep, bringing on bad dreams (or "nightmares").
The mare is often similar to the mythical creatures succubus and incubus.
The word "mare" comes (through Middle English mare) from Old English mære, mare, or mere, all feminine nouns. These in turn come from Common Germanic *marōn. *Marōn is the source of Old Norse: mara, from which are derived Swedish: mara; Icelandic: mara; Faroese: marra; Danish: mare; Norwegian: mare/mara, Dutch: (nacht)merrie, and German: (Nacht)mahr. The -mar in French cauchemar ("nightmare") is borrowed from the Germanic through Old French mare.