The scrips traded on BSE have been classified into various groups.
BSE has, for the guidance and benefit of the investors, classified the scrips in the Equity Segment into 'A', ‘B’,'T', ‘S', ‘TS' and 'Z' groups on certain qualitative and quantitative parameters.
The "F" Group represents the Fixed Income Securities.
The "T" Group represents scrips which are settled on a trade-to-trade basis as a surveillance measure.
The "S" Group represents scrips forming part of the "BSE-Indonext" segment.
The "TS" Group consists of scrips in the "BSE-Indonext" segment, which are settled on a trade-to- trade basis as a surveillance measure.
Trading in Government Securities by the retail investors is done under the "G" group.
The 'Z' group was introduced by BSE in July 1999 and includes companies which have failed to comply with its listing requirements and/or have failed to resolve investor complaints and/or have not made the required arrangements with both the depositories, viz., Central Depository Services (I) Ltd. (CDSL) and National Securities Depository Ltd. (NSDL) for dematerialization of their securities.
Source & more details at: http://www.bseindia.com/about/tradnset.asp#group