AK meaning in Military and Defence ?

The AK-47, officially known as the Avtomat Kalashnikova (Russian: Автома́т Кала́шникова, lit. 'Kalashnikov's automatic rifle'; also known as the Kalashnikov or just AK), is a gas-operated assault rifle that is chambered for the 7.62×39mm cartridge. Developed in the Soviet Union by Russian small-arms designer Mikhail Kalashnikov, it is the originating firearm of the Kalashnikov (or "AK") family of rifles. After more than seven decades, the AK-47 model and its variants remain the most popular and widely used rifles in the world.

The number "47" refers to the year the rifle was finished. Design work on the AK-47 began in 1945. It was presented for official military trials the following year in 1947, and, in 1948, the fixed-stock version was introduced into active service for selected units of the Soviet Army. In early 1949, the AK was officially accepted by the Soviet Armed Forces and used by the majority of the member states of the Warsaw Pact.

The model and its variants owe their global popularity to their reliability under harsh conditions, low production cost (compared to contemporary weapons), availability in virtually every geographic region, and ease of use. The AK has been manufactured in many countries, and has seen service with armed forces as well as irregular forces and insurgencies throughout the world. As of 2004, "[o]f the estimated 500 million firearms worldwide, approximately 100 million belong to the Kalashnikov family, three-quarters of which are AK-47s". The model is the basis for the development of many other types of individual, crew-served and specialised firearms.