Some occasions on which an investor can receive lump sum money include the annual performance bonus, Diwali bonus, full and final settlement amount from the previous job, signup bonus, Income Tax Refund (ITR), cash gift during festival/anniversary/birthday/marriage, etc., maturity/redemption proceeds from financial products, winnings from some contest/sport/competition, etc.
As the article above discusses, an investor may park the lumpsum amount in a debt fund. They can start an STP, wherein a small amount will be regularly transferred to a diversified equity fund over a period of time.