The Indian equity market has a long history and there are many participants in it. These participants include retail traders / investors, institutions (Domestic as well as Overseas), prop desks, arbitrageurs, hedgers, etc. Retail participants invest in the market both directly and indirectly through institutions. These institutions are known as Domestic Institutional Investors (DIIs) and comprise of Mutual Funds, Banks, Insurance companies etc.
On the other hand, Foreign Institutional Investors (FIIs) or Foreign Portfolio Investors (FPIs) are overseas entities registered in India and allowed to invest in the Indian stock markets. They play an important role in our market as they hold a decent chunk of overall investment in Indian equities.
FII activity in cash market segment should not be traced as a trading signal because they invest with long term perspective mainly. This data should be used as a helping tool for forming a positional view on the market. For short term trading their future & options activity should be tracked.