What does 'Custom Targeting' mean?

If Video Solutions is enabled in your network, you can add key values, audience segmentation, or content metadata in custom targeting for video line items. Line items that target those key values are eligible to serve for an ad request that comes in from one of your web pages or an app that has vital importance in its ad tags. Key-values, in particular, can be utilized for purposes that aren't covered by Ad Manager's built-in targeting. For example, fundamental values can be used to identify specific ad inventory on web pages or applications, or they can be used to target advertising depending on the information gathered from website or app visitors. Like other types of targeting, key values assist your advertising and purchasers reach their desired demographic.