Hi Ashishm,
The categorization is based on what the stock represents. As far as I know, NSE does not categorise stocks into groups. NSE has different series, each series representing a certain category. More on NSE's categorization here: Click on complete list in current market reports and under Securities in rolling (EQ) and trade for trade (BE,BT).
However, BSE categorises the Equity segment into 'A', 'B', 'T' & 'Z' categories where:
* The A group contains the list of the most popular stocks. Stocks that are actively traded. More on how stocks are categorised onto the 'A' group here.
* The Z group consits of Equity stocks which are blacklisted for not following Exchange rules & regulations or has pending investor complaints or any such reason.
* The T group consists of stocks that form part of the Trade to trade segment. Trade for Trade segment is a segment on which no intraday trading is allowed. All trades result in delivery.
* The B category includes stocks which don't form part of any of the above Equity groups.
* Additionally BSE also has the F group which denotes the Debt market segment.
* M/MT group consist of stocks forming part of BSE's SME (Small & Medium enterprise)
* G group consists of Governement securities available for retail investors.
* I group consists of Interest rate underlying.
* E group consisting of ETF's (Exchange Traded Funds)
You can view them on the Trading platform. Screenshot below:
Update
With effect from July 01, 2018, both NSE and BSE will be discontinuing IL series (institutional trading series). Under a window in this series institutional trades were allowed trade among themselves in scrips that had exhausted the foreign holdings limit. Read more.
Hope this helps :)