This article will explain what the function union and intersection does in your filter. These will show various places around workbook.
Let us take an example in which you look at the weekly schedule.
You are filtering by Team: Developer, Position: Developer.
Union will include everyone, in both the development team and the people in the company who has the developer position.
Intersection on the other hand, will only show the people who are both on the developer team and who has the position developer.