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Net 30 Days
This relates to a type of payment term. A company which has to pay its accounts on 'net 30 day' terms has thirty days following the date of the invoice to pay for goods or services received. Similarly a company paying its accounts on 'net 60 days' has sixty days following the date of invoice to pay etc.

http://www.blinco.com/solutions/glossary/schainae.htm

A cash discount is an allowance extended to encourage payment of invoice on or before a stated date which is earlier than the NET date. The percent of discount allowed is as agreed between buyer and seller and is often established by industry or trade custom. Usual discounts are 1/2, 1, or 2 percent with occasional discount allowances to 10 percent. Typical cash discount terms are shown below:

2 percent e.o.m. - 10: 2 percent discount allowed if paid on or before the 10th of the following month.

2 percent 1-60X or 2 percent 10-60 extra: 2 percent discount allowed if paid on or before the 70th day.

2 percent 10th prox.: same as 2 percent e.o.m. 10.

2 percent 10th 25th or 2 percent 25th 10: 2 percent discount allowed for payment on or before the 25th of the month f or billings of the first half of the month; 2 percent discount allowed for payment on or before the 10th of the succeeding month for billings of the last half of the month.

Note: Discount payment dates, other than with e.o.m. or prox. terms, are interpreted in various ways. The usual interpretation is that the discount date is calculated from the invoice date. Other interpretations should be specifically agreed upon between the buyer and seller. Other interpretations are based on a) the date goods are shipped, b) the date goods are received by the buyer, and c) the date the goods are inspected and found acceptable by the buyer.

Discount payment terms usually are stated in conjunction with a net term. Typical are:

1 percent 10 days, net 30 or 1-10-30

2 percent 10 days, net 60 or 2-10-60

2 percent 10 days 60 extra, net 90 or

2-10-60X net 90

2 percent 30 net 31

Where the net date is not stated in conjunction with a discount date, the presumption is that the invoice is due net the day following the discount date.
Net terms require that vendors' invoices be paid without discount on or before due date. Typical statements of net terms are:

Net: payment due immediately.

Net 10 days: due on or before the tenth day.

Net e.o.m.: due on or before the end of the month.

Net e.o.m. 10. net 10 e.o.m. or net 10th prox: due on or before the 10th of the month following.

Net 10-60X or net 10-60 extra: due on or before the 70th day.

Net 10th 25th or net 25th 10th: payment due on the 25th of the month for billings of the first half month; due on the 10th of the following month for billings of the last half of the month.