Urdu is one of the official languages of Pakistan, jointly with English, and it is also spoken in India, Bangladesh and Nepal. It has about 100 million speakers altogether, but for most people this is as a second or even third language. Despite its official status in Pakistan, only about 8% of the population speak it is as their native language, meaning it is not the most widely spoken language. In fact it only comes in at 5th place!
A descendant from Proto-Indo-European, it is very closely related to Hindi, and the two spoken languages are mutually intelligible. The main differences between them are the ways in which they are written: Hindi is written with the Devangari script, and reads left to right, whereas Urdu is written using the Persian-Arabic script, and like Arabic it reads from right to left.