SIP - Systematic Investment Plan is just a way of investing in Mutual Funds.

There are two ways in which you can invest in Mutual Funds:

1. Lump Sum - When you want to invest all your money in one shot in a mutual fund scheme. Eg. Investing 50K in a mutual fund scheme in one shot.
2. SIP - When you invest a certain amount regularly in a mutual fund scheme. Eg. Investing 5K per month in a mutual fund scheme for 6 months.

Lump Sum vs SIP is kind of similar to Fixed Deposit (FD) vs Recurring Deposit (RD). In FD, you deposit all your money on one shot while in RD, you deposit on a regular basis for few months.

As far as security or risk is concerned, Mutual Funds are subject to market risks whether you invest through SIP or Lump Sum. Underlying risk is determined by the scheme your are investing in.

Originally answered on Quora.