Cash or Equity refers to buying shares in equity market segment. They can be traded like futures which are contracts based on some of these equity shares. The main advantage in futures trading is low margin amount required, ability to carry forward short positions. Equity shares can be bought in a minimum of 1 share where are futures have fixed number of shares (lot size). For example Reliance has a lot size of 250 in futures whereas even 1 share can be bought in cash market.