Topics are terms that describe the brands and/or concepts that you want to track online. These determine how data will be organized and visualized in graphs in Radarr by Genesys. 
Sub-topics are the brands or themes organized under particular topics. 

E.g.: 

Topic: Fruits 

1. Sub–Topic: Banana 

2. Sub–Topic: Apple 

3. Sub–Topic: Grape 

Topic: Countries 

1. Sub–Topic: Singapore 

2. Sub–Topic: Malaysia 

The below picture illustrates where Topic and Sub-topic labels are entered in the Query Builder. 

Fig: Topic and Sub-topic