What is the difference between submissions and submission storage?

I am considering purchasing a premium Jotform plan but am confused about the difference between submissions and submission storage. The free plan allows for 100 submissions and a total submission storage of 500. What is the 'total submission storage'?

Monthly submissions are the number you received through all forms in a single calendar month.  Stored submissions are the number you are stored between all forms.  If you receive  100 submissions per month for 5 months, you would have 500 stored submissions if none were deleted. 

The total stored can be reduced by deleting submissions.  The monthly total cannot be reduced other than by the monthly reset.