Bilberry
Bilberry is a name given to several species of low-growing shrubs in the genus Vaccinium (family Ericaceae) that bear tasty fruits. The species most often referred to is Vaccinium myrtillus L., also known as blaeberry, whortleberry, whinberry (or winberry), myrtle blueberry, fraughan, and probably other names regionally. They were called black-hearts in 19th century southern England, according to Thomas Hardy's 1878 novel, The Return of the Native, (pg. 311, Oxford World's Classics edition).
The word bilberry is also sometimes used in the common names of other species of the genus, including Vaccinium uliginosum L. (bog bilberry, bog blueberry, bog whortleberry, bog huckleberry, northern bilberry), Vaccinium caespitosum Michx. (dwarf bilberry), Vaccinium deliciosum Piper (Cascade bilberry), Vaccinium membranaceum (mountain bilberry, black mountain huckleberry, black huckleberry, twin-leaved huckleberry), and Vaccinium ovalifolium (oval-leafed blueberry, oval-leaved bilberry, mountain blueberry, high-bush blueberry).
Bilberries are found in damp, acidic soils throughout the temperate and subarctic regions of the world. They are closely related to North American wild and cultivated blueberries and huckleberries in the genus Vaccinium. The easiest way to distinguish the bilberry is that it produces single or pairs of berries on the bush instead of clusters like the blueberry. Another way to distinguish them is that while blueberry fruit meat is light green, bilberry is red or purple. In this way you can also distinguish the bilberry eater from the blueberry eater by his red fingers and lips. Bilberry is used as a food plant by the larvae of some Lepidoptera species - see list of Lepidoptera which feed on Vaccinium.
Bilberries are rarely cultivated but fruits are sometimes collected from wild plants growing on publicly accessible lands, notably in Fennoscandia, Scotland, Ireland and Poland. Notice that in Fennoscandia, it is an everyman's right to collect bilberries, irrespective of land ownership. In Ireland  the fruit is known as fraughan in English, from the Irish fraochan, and is traditionally gathered on the last Sunday in July, known as Fraughan Sunday.
Bilberries were also collected at Lughnassadh in August, the first traditional harvest festival of the year, as celebrated by the Gaelic people.  The crop of bilberries was said to indicate how well the rest of the crops would fare in their harvests later in the year.
The fruits can be eaten fresh, but are more usually made into jams, fools, juices or pies.  In France they are used as a base for liqueurs and are a popular flavouring for sorbets and other desserts.  In Brittany they are often used as a flavouring for crepes, and in the Vosges and the Massif Central bilberry tart (tarte aux myrtilles) is the most traditional dessert.

# Medicinal uses
Bilberry is often said to improve night vision, and the story is told of RAF pilots in World War II using bilberry for that purpose. A recent study  by the U.S. Navy found no effect, however, and the origins of the RAF story are unclear; it does not appear to be well known in the RAF itself.. Studies (, ) have shown that bilberry can reduce or reverse effects of degenerative eye disorders such as macular degeneration. The overall therapeutic use of bilberry is still clinically unproven.
On the other hand, the RAF story about bilberries was more likely a cover to conceal the British access to radar, still an official secret at the time of World War II.  See, for example: 
It may have other beneficial effects on capillaries due to the strong antioxidant properties of its anthocyanidin flavonoids.
The leaves have historically been used to treat gastrointestinal ailments, applied topically or made into infusions.  The effects claimed have not been reproduced in the laboratory, however.