This movie/ video explains the concept of protective put in the CFA exam. If you are not familiar with put options, please refer to the "Introduction to Put Option". The following is the transcript.

Now we continue to discuss the concept of protective put. To understand the concept of the protective put, it is better to understand the motivation of forming a protective put strategy. Assume you are holding a stock S. It was purchased at S0 (e.g. $20). Now it has appreciated to $30 and you have unrealized gain of $30-$20=$10. That’s great! But you have concern. Now the stock becomes more volatile as the price gets higher. You still expect it to rise (hopefully) but you are afraid of the downward risk. What can you do? One of the strategies is to form a protective put. This is done by purchasing a put option with exercise price X = $30. With the protective put option, you will be able to secure almost all the gain. Why? Let’s assume the put option is priced at $2. Recalling that a protective put has a shape like this. With the X = $30, the breakeven point of the put option is $30-$2 = $28. The put option is sloping in the opposite direction of the stock when the stock price is less than the X. This means when the stock decreases $1, the value of the put option increases $1. As a result, your unrealized gain is protected! Of course, since you paid $2 premium, you can only “protect” $8 of the unrealized gain. What if the stock is higher than $30? When this happens, you won’t exercise the option as it is “out-of-money”. So again you capped the loss of the put option at $2. But the stock will have unlimited gain. Therefore, by combing the stock and the put option, you also realize a strategy equivalent to buying a call option – limited loss but unlimited gain.