Inverse ETF are basically known as "Short ETF," or "Bear ETF" and no inverse ETF's trade in India, so you can sell NIFTY FUTURES with 100 percent cash margin, which is equivalent to inverse ETF for NIFTY.
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Inverse ETF's are not available in India.
Basically similar to how your profit from buying Nifty ETF if market goes up, you could have profited by buying Nifty Inverse ETF if market had come down.
This is how investopedia defines it:
An exchange-traded fund (ETF) that is constructed by using various derivatives for the purpose of profiting from a decline in the value of an underlying benchmark. Investing in these ETFs is similar to holding various short positions, or using a combination of advanced investment strategies to profit from falling prices.