If you have a large sum of money lying idle for a day or two, you can neither put it in a fixed deposit (FD) account nor in any long-term option like equity mutual fund (MF) to fetch some decent return.
What you may explore is debt mutual funds, as such funds are considered safer for short-term investments because they remain unaffected by daily fluctuations in the equity markets. However, debt funds are also subject to some other risks, like interest rate risk, credit risk etc due to fluctuations in interest rates and trading of debt papers in secondary markets.