Terms of Payment

I have two TOPu2019s One with the day limit 10 and another one with day limit 31.

What is this Day limit ?

Can anybody explain me the day limit 10 & day limit 31

Also what is the relevance of the fields under Base line date calculation

Fixed Day

Additional months

It would be great if the following fields under the payment Terms tab also the following fields.

No of Days field

Fixed date

Additional months