30% off or 30% discount
Calcoulation is 1000*(1-25%)=750
I will give you 25% discount,that will be 750.
Please notice,discount has another meaning in Accounting--贴现,折现
This is more professional and will help you earilier to understand the meaning of "discount".
According to your question,I will give you 25% DISCOUNT to make you buy my goods.So the cost of mine is 25% discount(250)
Such example please refer following:
We give 10 percent discount for cash.
现金付款,我们九折优惠.