What do the payment terms 1% 10-25th mean?

Answer 1

It means you get a 1% discount if you pay in TEN DAYS, but the bill is due on the 25th of the closest month.

Examples:

1% 10TH/25TH = 1% discount if paid by the 10th, due the 25th.
1% 10/30 = 1% discount if paid in 10 days, due in 30 days
1% 10TH/30 = 1% discount if paid by the 10th, due in 30 days.

Answer 2

That means you get a 1% discount off of your total bill if it is paid by the 10th through the 25th.