A lumpsum investment means putting your entire amount into a fund in one go, instead of spreading it across smaller amounts over time. You invest the full sum at once and buy units at the applicable NAV.
How is a lumpsum different from an SIP?
The other way to invest in a mutual fund is a Systematic Investment Plan (SIP) — a fixed amount invested at regular intervals, such as every month, instead of the whole amount at once. A lumpsum suits money you already have and are ready to invest now; an SIP suits investing gradually out of your regular income. You can read more in What is SIP?.
How do I invest a lumpsum on Rupeezy?
On Rupeezy, open any fund's page and choose the One Time option to place a lumpsum order — you enter the amount and pay in a single step. For the full walkthrough, see How to place a lumpsum order on Rupeezy?.