Dynamic Audiences allow you to define an audience based on the traits of your customers. As the traits change, the customer will move into or out of the audience.
Case Sensitivity of Traits
Note that when creating a dynamic audience, the selection by traits is case sensitive. You must ensure that if you are using a trait to look up customers you pass the data to us in a normalised manner so as not to miss out on selecting the correct audience. e.g. UK Postcode has a standard format that is all upper case, if you send us data with mixed or lower case, you will have to create a more complex dynamic audience definition to select all the different postcodes that may have been submitted instead of a single example of Require Customer Postcode start with PE, you would need to include all the different options if you data isn't normalised.