This determines which participants are considered part of the same team - which fields do they have in common. 

Most commonly this would be Contest and Club, but may for example also include Gender if you should have separate Male & Female teams. 

The Aggregation fields may also take a function or expression, for example when using the Team Lap Race mode you may also score individuals in the same way but here the aggregation should be an individual based on the bib and use the standard club field for teams of 2 or more.