Elves were sometimes thought to be male faeries -- in England, this especially applied to small faery boys. In general, the term 'elf' in England referred to the smaller trooping faeries, although in Scotland, elves were human sized, and Faeryland was called 'Elfame.'
In Scandanavia, faeries were also called elves, and were either light elves or dark elves, similar to the Scottish Seelie and Unseelie Courts. The light elves were like England's trooping faeries, and in Christian times, Scandanavian elves (or huldre folk) destroyed cattle, stole humans away, and avenged any injuries done to them in the same way that the Scottish faeries did. Huldre maidens dressed in grey with white veils, and were beautiful but had long cows' tails. If a man was dancing with a huldre girl and noticed her tail, he must not betray her, but instead tactfully mention that she was losing her garter. He would then be rewarded by perpetual prosperity.
Danish elves loved to steal human food, such as dough. Though beautiful from the front, Danish elves or ellewomen were hollow from behind.
Publications such as Goedys' Lady's Book, published by Louis A Goedy, popularised the idea of the Christmas elf in the nineteenth century, and JRR Tolkien's famous The Hobbit brought elves into high fantasy in the twentieth century.
Bibliography: An Encyclopedia of Fairies, by Katharine Briggs.
Webography: Wikipedia: http://en.wikipedia.org/wiki/Elves.
Picture courtesy of Google Images: https://www.google.com/search?hl=en&site=imghp&tbm=isch&source=hp&biw=1024&bih=600&q=elf&oq=elf&gs_l=img.3..0l10.1727.1949.0.2324.3.3.0.0.0.0.112.264.2j1.3.0....0...1ac.1.24.img..0.3.264.r2OyC5CcxgE.
There are two broad types of faery: the Seelie Court and the Unseelie Court, 'seelie' and 'unseelie' being Scottish in nature. The Seelie Court are the 'good' faeries (though one would never want to anger them, and even 'good' faeries can be vengeful), whilst the Unseelie Court are the 'bad' faeries. 'Seelie' means 'happy,' 'blessed,' or 'lucky,' according to Wikipedia (http://en.wikipedia.org/wiki/Seelie_Court).
'The Shining Throng,' 'The Golden Ones,' and 'The Light Court' are other names for the Seelie Court, according to Wikipedia (http://en.wikipedia.org/wiki/Classifications_of_fairies#Seelie_and_Unseelie_Courts).
Seelie are (mostly) benevolent, asking humans for help and helping them in turn. They are most often seen at twilight.
'The Host' are members of the Unseelie Court who fly through the night, capturing hapless victims, beating them and forcing them to participate in the Unseelies' activities, which include shooting other men and livestock with elf-shot.
There is also a collection of 'weird and terrifying monstrosities' who belong to the Unseelie Court, according to Froud and Lee (Faeries); these monstrosities are often associated with particular localities.
