This original song made by Pakistanis was called "Thayya Thayya" and sung in Punjabi. If you listen to it you might recognize the first word Eid, an Islamic celebration. The singer is saying that his love did not come on Eid and is asking her to come back and basically singing about their love.
Allah Rakha Rahman, an Indian convert to Islam, remade the song into "Chaiyya Chaiyya" which means shadow, and is sung in Urdu, a more Islamic form of Hindi, since it is more usually spoken by Muslims in India and Pakistan. In fact, Bollywood prefers to use Urdu, as it is the language that is more recognized and respected throught South Asia, but proper Urdu and Hindi are very different. A bit off topic, but although Urdu is the official language of Pakistan, it is only 8% of the populations language at home, almost half the population speaks Punjabi, as do many Sikh and other groups in India. Hindi, though it sounds like the word Hindu as in the foollwers of the religion, is just a language, and Muslims in India speak it as well as Hindus.
Dil Se roughly translates to "from the heart". Allah Rakha Rahman also comppsed all the other songs of the movie and has many other great songs to his credit as well, so buying the soundtrack is definitey worth it. Who knows, it may lead you to buy other soundtracks of Bollywood movies he has directed. He even helped with The Lord of The Rings musical and Broadway hit Bollywood dreams.
The music video to the song was a big hit, as well as the song, and features the main actor Shah Rukh Khan, ultimate top superstar of Bollywod, dancing with Indian model, Malaika Arora. The video has them dancing on top of a train (which the song is supposed to sound like) amid a beautiful backdrop of sensational scenery in the hill station Ooty, located in the sate of Tmail Nadu, India.
Neither of the actors actually sings the song which is the case for almost all Bollywood films. Instead they have professional playback singers who sing the songs and the actors just lip synch and dance to them. The actual singers are Sukhwinder Singh (male) and Sapna Aswathi (female vocals).
You could find a translation by searching for it (try the link: [...]). Since I've gone on long enough about one song, I'll just translate a little and explain the gist of the song according to the movie. The man has met a woman (not the woman singing with him on the train) and he sings about her and her attributes. For example, he says "she is like fragrance" (khushboo)and her language is like Urdu, since it considered a beautiful and poetic language in South Asia. Chayya means shadow. The song is about those whose heads are under the shadow of love and he's telling people to come to the shadows (of love). If you have a good ear you can make out the Arabic term for paradise JUNNAT since loving is like being in heaven.
