In Relation to Discount Terms, What Does 2/10, N/30 Mean

In relation to discount terms, what does 2/10, n/30 mean?

A) Invoice due on 2^nd October or 30 November
B) 2 10ths = 20% discount, not 30%
C) 20% discount, November 30th
D) 2% discount to be deducted from the invoice price if payment is made within 10 days or the full amount is due within 30 days of the invoice date