The business domains are already predefined domains, i.e age, gender, address etc. If you would like to add custom domain, it can be added in Domains>Customs:
There the Name, Condition and Threshold should be defined for the given domain.Please note that the threshold is a minimal percentage of input records that belong to the domain and satisfy the condition. This custom domain will be displayed in Domains:
Let me know if the provided information is sufficient and do not hesitate to ask if you have further questions.