South Asia comprises those countries lying between the Himalaya range of mountains and the Indian Ocean (north to south) and between the Ganga and Indus river valleys (east to west). The Indian Ocean shoreline is divided between the Arabian Sea (in the west) and the Bay of Bengal (in the east). The extensive, triangular-shaped landmass of South Asia is sometimes referred to as "the Indian Subcontinent", or simply "the Subcontinent"
Afghanistan is not considered part of the region, but often involves itself in South Asian regional organisations.
Some commonalities exist to this area, mainly climate and culture.
Climate: Apart from the Himalaya, the climate is tropical, with monsoon in summer and dry winter. However, you have the extremes of this climate, i.e. in Western Pakistan monsoon is quite non-existent and in Southern India, it lasts for six months. Sri Lanka even has two monsoons, one in May, one in October/November.
Culture: The influence of historical Indian culture can be seen everywhere. Two of the main "world religions" have their origins within South Asia: Hinduism and Buddhism. A third, Islam, was introduced by Muslim invaders starting around the 7th century and rose to prominence during the Mughal Empire.
An additional layer of South Asian cultural unification derives from the influence of British culture, and especially the frequent and growing use of the English language, as a result of India having formed the "Jewel in the Crown" of the British Empire before Independence in 1947.
Population density: South Asia is one of the world's most densely populated regions - approximately 1.6 billion people (or roughly a quarter of humanity) make their home there. The average population density of 305 people per square km is 7 times the world average.
The region does not have a lingua franca. However, as much of South Asia was under British rule, English is widely spoken by educated people. Hindi and Urdu are spoken over much of India and Pakistan. As the two languages are mutually intelligible, if you have to learn one before visiting, pick one of these. Hindi will also help you in Nepal, as the Nepali language is quite similar. Bengali is another major language spoken in Bangladesh, West Bengal and understood in some other eastern states of India.
Other than these, South Asia has a fascinating diversity of languages. India, in particular, is home to hundreds of them, and Pakistan too has quite a few. In the major cities and tourist destinations, you will be able to get by with English with varying degrees of difficulty.
International airports include:
The number of direct flights between India and U.S/U.K is increasing.
For most countries in the region, haggling is essential while shopping--see How to haggle.