Trows (or sometimes "Trow" in plural) are a type of goblin found in the folklore of the Shetland and Orkney Isles - they are also similiar to the Norse trolls but tend to be shy and extremely small, however they are also known to be troublesome and only able to appear during the hours of the night.
Trows would enter people's homes and cause mischief or play tricks and pranks but were also known to go as far as kidnapping humans - especially musicians, due to their legendary love of music.
Although Trows are considered a dangerous and mischievous fairy they are not entirely without merit and when caught in a good mood they are said to teach humans magic as well as fiddle tunes.
Due to their rather mischievous nature rather than malice they are similar to the Nuggles, another Shetland exclusive fairy.
The word "Trow" is itself simply a variant of the word "troll" and for many centuries Shetland and Orkney belonged to the Norse before being given to Britain as part of a marriage dowry - as such Trows are an amalgamation of the original Norse Trolls and Goblins, thus have developed the Goblins sense of mischief and the Trolls general solitary lifestyle and capability for greater harm (if provoked).