Which type of tax was reduced after 1991?

Marginal tax rate was reduced after the 1991-92 tax reforms. During this reform, the marginal tax rate was brought down to 40%. In 1996-97, there were further tax reforms which brought down the marginal tax rate to 35%. You can read about the Tax Administration Reform Commission – TARC. Mandate, Report, Recommendations in the given link.

Further readings:

1. Tax Policy Council & Tax Policy Research Unit: Notes for UPSC
2. Taxation in India – Direct taxes & Indirect Taxes, Features of Taxation System