A balaclava (pronounced /ˌbæləˈklɑːvə/), also known as a balaclava helmet or ski mask, is a form of headgear that covers the whole head, exposing only the face or upper part of it, and sometimes only the eyes. The name "balaclava" comes from the town of Balaklava, near Sevastopol in Crimea, Ukraine. During the Crimean War, knitted balaclavas were sent over to the British troops to help protect them from the bitter cold weather. However, according to Richard Rutt, the name 'balaclava helmet' did not first appear in print during the Crimean War, but only much later, in 1881. . This type of headgear was also known in the 19th century as an Uhlan cap or a Templar cap.. In modern American English,when made for those serving in the armed forces, they are usually known as 'helmet liners'.  They are traditionally knitted from wool, and can be rolled up into a hat to cover just the crown of the head.
Modern balaclavas can be made from a number of materials, such as silk, cotton, polypropylene, neoprene, wool, acrylic or fleece. Modern balaclavas are also used in outdoor winter sports activities such as skiing, snowboarding, snowmobiling, running or winter bicycling to help protect the face from the cold wind and maintain warmth. Motorcyclists also wear one under their safety helmets for similar reasons; balaclavas also help to keep the inner lining of the helmet clean.
Most commonly firefighters will wear a fire resistant balaclava, otherwise known as a Nomex Hood, when responding to a fire call along with their SCBA and Bunker Gear. This Balaclava covers the head and neck, with an open face; typically covered by the mask portion of the SCBA. This is used to help minimize the risk of potentially fatal burns to the upper back, neck, scalp and face.
Racing drivers must wear balaclavas made of fire-retardant material underneath their crash helmets in order to improve protection in case of a fire following an accident, and commonly cover the nose and mouth to reduce inhalation of smoke and fumes. Dragster-racing drivers usually wear balaclavas which have just two separate eye holes because of the increased fire risk.
In the Indian subcontinent, balaclavas are commonly referred to as monkey caps, due to their typical earth tone colours, and the fact that they blot out most human facial features. Monkey caps sometimes have a small, decorative, woollen pom-pon on top. They are commonly worn by troops on Himalayan duty.
British Police in Kent confiscated the War on Terror board game partly due to the inclusion of a balaclava. Police said it "could be used to conceal someone's identity or could be used in the course of a criminal act".
A balaclava may also be used for concealment purposes, in the course of illegal activities by criminals, and occupationally by SWAT and Special Forces personnel. It may also be used by Irregular military forces or paramilitary organizations to conceal their identities.