Discount refers to the price of a bond when it is below its par value.
Derivative is a type of security whose value is “derived” from an underlying asset. (Eg; Futures and Options).
A depression is a recessionary decline in real GDP (taking inflation into account) greater than 10% lasting at least 3 years.
Delta is also called the hedge ratio, which is the ratio of the change in price of an option to the change in price of the underlying stock.