When you include a link in an ad you have the option to add a description. When your ad appears in the News Feed placement the description will show dynamically. This means the description will only show in your ad if it’s likely to appeal to the person seeing it.
This only applies to ads using the single media ad format and which appear in the Facebook News Feed. This does not apply to dynamic creative ads.
This feature can help improve the performance of your ad. For example, some people are more likely to take an action, such as making a purchase, when they see the price of an item directly in an ad. Others are more likely to make a purchase when they see the price only after interacting with an ad. We’ll decide whether or not to show your description based on what we think will most impact each person and cause them to take a meaningful action.
Some people will see the description and some people won’t. Because the description may not show at all, you should only put non-essential information there. Put essential information in the headline, such as shipping information, detailed product information (like the type of material or product dimensions), ratings, reviews, or your return policy.