A form of data storage that consists of a pair of linked items. The key is a unique identifier for an item of data, and the value is the data that's identified by the key. For example, you might set
headline_1 as the key for the text that appears in a text box in a creative. The value associated with this key might be
Summer deals available now! which is the actual text that displays in the ad when the
headline_1 key is called in your code.