A SIP, or Systematic Investment Plan, is a standing instruction to invest a fixed sum into a mutual fund on a set date each month, or sometimes weekly. The money is debited automatically and buys units at that day's NAV. When the market is down you get more units for the same rupees, and when it is up you get fewer, which averages your purchase cost over time. Suppose you set a ₹5,000 monthly SIP in a Nifty 50 index fund. Over years you accumulate units without needing to decide when to invest, which removes the timing problem that trips up most people. SIPs do not protect you from a falling market; the value of your holdings falls with it. What they provide is discipline and a low-cost way to build a long-term position. Many brokers also offer stock SIPs for buying shares in the same way.