Marketing list contain the members like Account, Contact or Lead records. You can add the MappyField 365 data in any marketing list to market the specific segments more effectively.
By clicking on ‘Marketing List’ icon under the “Select Entity” option, you will get the Add to Marketing List popup window. 
You can get the “Marketing List” by clicking on Search icon if it has already been created in Marketing -> Marketing List or you can add to a new list by selecting the “Add to a new list”. 
Note: At a time only the single entity records can be assigned to the Marketing List.