"Chai" is the Hindi word for "tea", which in turn comes from "cha", the Chinese word. The term describes a mix of black tea mixed with strong spices including cinnamon, cloves, ginger, cardamom and black pepper.
Usually it is then mixed with warm milk and sweetened. A version of spiced drink has been used in India for more than 5,000 years, when it was developed for use in ayurvedic medicine, but original versions of masala chai didn’t include black tea at all. That was an innovation introduced after the British popularized tea.
Chai culture is ubiquitous in India, found on trains, streets, smart hotels and private homes. If you think Starbucks or Caffe Nero are common, they have nothing on the number of chai vendors.
Although the basic ingredients are the same everywhere, the specific spicing varies from region to region. One difference from western tea is that the tea leaves are usually boiled twice, once before and then once after the milk and sugar has been added.
Chai Lattes have only taken off in recent years, but chai prepared with milk has been around for at least a century.