The Custom tab includes tags specific to that individual. You can add tags through our Custom attributes feature. Custom Attributes allow you to tag/group your audience in specific ways. For example, if you want to distinguish your weekly email list from your donor email list, here is where you create tags for those groups.
Custom attributes can be found under the Settings tab > General > New Custom Attributes. Custom attributes are located in the Custom tab of every profile and both attributes and attribute categories can be edited at any time.