Goblin is a general term that can apply either to the ugliest members of the fae, or to certain sub-races. Those included the Scottish Trows, English Spriggans, Welsh Knockers, Cornish Knockers, German Kobolds and Wichtlein, the Irish Phooka and even Shakespeare's infamous Puck .
According to some tales or mythology, goblin comes from Gob or Ghob, who happened to be the king of the gnomes, His inferiors were called Ghob-lings.
Though "The Concise Oxford Dictionary of Current English" the name is probably derived from the Anglo-Norman language gobelin (medieval Latin gobelinus), which is probably a diminutive of Gobel, a name related to the word kobold. Goblin is also related to the French lutin.
Goblins belong to the Unseelie Court, and are at war with fairies. In some circles, Goblins are considered to be the cousins of gnomes, except there is a belief that gnomes are stupid and that no one in their right mind would confuse the two.
Goblins grow up to 30 cm. They are covered with a thick coat of black/grey hair. Goblins can usually be found wearing very dark colored cloths, plus a tall cap similar to that of the Gnome. They can appear as animals. They have a somewhat bestial or grotesque appearance: their brow is fully covered with thick hair and their mouth filled with yellowed, crooked teeth. Female goblins are referred to as "hags" or "crones". They mimic human actions in their sardonic way, twisting human rituals and culture to show the worst aspects. In recent depictions, Goblins have been portrayed as green in color, though there is no proof they ever were colored this way.
Goblins are associated with Earth, which is close to Death. But they are said to correlate with fire, or have the ability to create it too.
Goblins are pranksters. They rearrange items in the house, tangle up horses, bang pots and pans, strip humans of their clothing as they sleep, knock on doors and walls, and even dig up the graves and scatter the bones around. Goblins like to borrow horses and ride them all night. If a horse is tired in the morning, it is said a goblin rode it. This is also connected to witches too in legend. If a horse is panicking, the goblin is trying to mount it.
Goblin women steal human babies and replace them with ugly goblin babies (changelings). Goblin changelings are sometimes known as "oafs" or "crimbils".
Mine goblins make knocking noises by striking pickaxes and hammers against the stones. Some miners take the resulting sounds as a sign of good luck, that they are indicating presence of rich ore deposits. Others believe that they (Kobolds and Wichtlein) just imitate the miners to fool them. As a death companion he is sometimes accused to cause underground fires or warn for the coming deaths. To avoid the Knockers' wrath, a pastie (traditional miner meal) is always left out for them. It is said that a goblin’s smile can curdled blood, while a goblin’s laugh sours milk and causes fruit to fall from trees.
The English Hobgoblin loves to live in homes, making a lot of trouble for the people living there. Others reside in mines where they search for treasure, along for trouble. Still others of the family prefer grottos, often residing in the same one their entire life.
One myth puts the orgins of Goblins in France, in a cleft of the Pyrenees, from which they spread rapidly throughout Europe. They hitched a ride with Viking ships to Britain. Bryn y Ellyllon 'The Hill of the Goblins' is a place in Somerset. The Gap of Goeblin is a hole and underground tunnel in France.
JRR Tolkien based the orcs in The Hobbit on George Macdonald's portrayal of the creatures The Princess and the Goblin. He coined the word 'Orcs' for goblins in The Lord of the Rings.