Mabon is one of the eight solar holidays or Sabbats of American Neopaganism. It is celebrated on the autumnal equinox, which in the northern hemisphere is circa September 21 and in the southern hemisphere is circa March 21.
Also called Harvest Home or simply Autumn Equinox, this holiday is a ritual of thanksgiving for the fruits of the earth and a recognition of the need to share them to secure the blessings of the Goddess and God during the winter months.
Among the Sabbats, it is the second of the three harvest festivals, preceded by Lammas and followed by Samhain.
Mabon was not an authentic ancient festival either in name or date. The autumn equinox was not celebrated in Celtic countries, while all that is known about Anglo-Saxon customs of that time was that September was known as haleg-monath or 'holy month'.
The name Mabon has only been applied to the neo pagan festival of the autumn equinox very recently; the term was invented by Aidan Kelly in the 1970s as part of a religious studies project. (The use of Litha for the Summer Solstice is also attributed to Kelly). Previously, in Gardnerian Wicca the festival was simply known as the 'Autumnal Equinox', and many Neopagans still refer to it as such, or use alternative titles such as the neo-Druidical Aban Efed, a term invented by Iolo Morgannwg.
The name Mabon was chosen to impart a more authentic-sounding "Celtic" feel to the event, since all the other festivals either had names deriving from genuine tradition, or had names grafted on to them. The Spring Equinox had already been misleadingly termed 'Ostara', and so only the Autumn Equinox was left with a technical rather than an evocative title. Accordingly, the name Mabon was given to it, having been drawn (seemingly at random) from Welsh mythology.
The use of the name Mabon is much more prevalent in America than Britain, where many Neopagans are scornfully dismissive of it as a blatantly unauthentic practice. The increasing number of American Neopagan publications sold in Britain by such publishers as Llewellyn has however resulted in some British Neopagans adopting the term.