What is the difference between surplus stock and dead stock?

Surplus stock and dead stock are the two different types of business ,surplus stock is a immoderate stock which the company have within a limited time period.Dead stock is a stock which can't be sell or it is unsellable, it can be happen if the items are damaged or because of incorrect deliveries.Many companies use dead stock as a gift with a purchase or donating to charity because they don't want to pay tax.