Matka is a type of gambling

Gambling

Gambling is the wagering of money or something of material value on an event with an uncertain outcome with the primary intent of winning additional money and/or material goods...

 that originated in Mumbai, India. The word Matka is often used as a synonym for "gambling" in India. Matka is known to be started and made a big money proposition in India by Ratan Khatri

Ratan Khatri

Ratan Khatri is considered by many to be the pioneer of the gambling/betting movement in India. Khatri, who hails from a Sindhi family, started from humble beginnings and like most Hindu Sindhis living in India, he came to Mumbai from Karachi, Pakistan when he was a teenager during the 1947 partition...

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Matka is also known as Satta and is an ingenious system of gambling on numbers. Punters bet money on numbers (2 or 3 digit) and the winning number receives eighty times the sum wagered. However there are smaller wins too.

Current matka business in Mumbai

The Matka business in Mumbai(the hub city where this betting game originated) is currently run by small-time bookies primarily in the area of Kalyan and Mulund and there have been instances of criminal involvement. Ratan Khatri, quoted in an article in the Indian Express expressed his sentiment on the current scenario of Matka in the city, by saying that the game has lost its previous widespread appeal because the business has now been taken over by criminals.
There are currently around 400 matka bookies in the city and above 1,000 cross the state is fake