Systematic Investment Plan (SIP) is an approach to investing small amounts at regular intervals rather than investing lump sum amount at one time.
Considered to be the safest way to invest into Equity Markets by going the SIP route, Investor is not trying to capture the Highs and lows of the market, but trying to average the cost by investing at regular interval.
Concept is that, When the markets fall investor gets more units. Likewise investor acquires lesser units when the market goes up. This means that investor buys less when the price is high and investor buys more when the price is low. Hence the average cost per unit falls down over a period of time.