What do the credit terms, 2/15, n/30 mean?

• A two percent discount can be deducted if the invoice is paid before the fifteenth day following the date of the sale.

• A two percent discount can be deducted if the invoice is paid after the fifteenth day following the sale, but before the thirtieth day.

• A fifteen percent discount can be deducted if the invoice is paid within two days following the date of sale.

• A two percent discount can be deducted for a period up to thirty days following the date of sale.