A lumpsum investment pertains to a one-time commitment of funds into a specific mutual fund scheme. Essentially, when you invest a certain sum all at once, that's termed as a 'lumpsum' investment.
Now, an 'additional lumpsum' is when you decide to invest again in a scheme where you've already made a previous lumpsum investment. Every subsequent lumpsum investment after the first one in a particular scheme falls under this category. A highlight of this feature is that generally, the minimum amount for additional lumpsum investments is lower than the first-time lumpsum investment.
For instance, consider you've invested a lumpsum of ₹5,000 in 'Canara Robeco Small Cap Fund - Direct Plan - Growth Option', which is the scheme's minimum requirement. A few days later, if you decide to invest more in the same scheme, the minimum amount you can invest might be reduced, say, to ₹1,000, as an additional lumpsum.
Note: The minimum requirement for additional lumpsum investments can vary across different schemes.