A bear put spread is a type of options trading strategy that involves buying a put option at a higher strike price and simultaneously selling a put option at a lower strike price. The goal of this strategy is to profit from a moderate decrease in the price of the underlying asset.

A put option gives the holder the right, but not the obligation, to sell a certain number of shares of the underlying asset at a certain price, known as the strike price. When an investor buys a put option, they are betting that the price of the underlying asset will decrease below the strike price, allowing them to buy shares at a lower price and sell them at a profit.

In a bear put spread, the investor buys a put option at a higher strike price (also known as the "long put") and sells a put option at a lower strike price (also known as the "short put"). The difference between the two strike prices is known as the "spread."

For example, let's say an investor buys a put option at $50 strike price for $2 and simultaneously sells a put option at $45 strike price for $1. If the price of the underlying asset decreases below $45, the investor can exercise the long put option and buy shares at $45, earning a profit of $4 (the difference between the strike prices of $50 and $45) minus the cost of the options, $1.

However, if the price of the underlying asset doesn't decrease below $45, the investor will lose the $1 paid for the short put option, but will not lose anything more.

In summary, a bear put spread is a type of options trading strategy where an investor buys a put option at a higher strike price and simultaneously sells a put option at a lower strike price. The goal of this strategy is to profit from a moderate decrease in the price of the underlying asset and it has limited downside risk.