Relevance is what we call a summary index, because it combines Reach and Popularity to give you the best balance between these two indexes. So if you order by Relevance you will find on the top interests or psychographic traits that have a high Popularity but also the best reach within the category.
Tip: order by Relevance in the Interests section.
Why? Because especially when you are looking at a long list of specific brands, media or celebrities, if you order only by reach you will often find mainstream interests in the top results, for example in the top musicians you’ll always find Taylor Swift, Rihanna or Eminem. But if you order by Popularity you can end up focusing on interests that are too niche (have a too low reach).
So Relevance is the best solution because it shows you the interest that are distinctive of your audience but in the same time have a good Reach as we can see in the example below, if we are trying to find Lulemon’s audience favorite beauty products.