A government debt obligation (local or national) backed by the credit and taxing power of a country with very little risk of default.
This includes short-term Treasury bills, medium-term Treasury notes, and long-term Treasury bonds.
In India, the Central Government issues both, treasury bills and bonds or dated securities while the State Governments issue only bonds or dated securities, which are called the State Development Loans (SDLs). Government securities carry practically no risk of default and, hence, are called risk-free gilt-edged instruments. Government of India also issues savings instruments (Savings Bonds, National Saving Certificates (NSCs), etc.) or special securities (oil bonds, Food Corporation of India bonds, fertiliser bonds, power bonds, etc.). They are, usually not fully tradable and are, therefore, not eligible to be SLR securities.