The phrase "substantial discount" means a significant reduction in price. It indicates a large amount of money being saved on a purchase. Full definition
The bond principal and any remaining coupons (the residue) then trade separately from the strip of detached coupons, both at substantial discounts from par. (hsbc.ca)
And if you are deployed, you are also eligible for substantial discounts on top of that. (netquote.com)
Many insurance providers offer substantial discounts for drivers who voluntarily take a driver improvement course. (idrivesafely.com)