Top 3 share
How much of the visibility on page 1 the three most visible products hold together.
The visibility of the three most visible products divided by the visibility of all products on page 1 for your active keywords, in the selected period, using the same visibility as everywhere else. A high share means a few products dominate the page. A low share means visibility is spread across many products. The change is in percentage points against the previous period of the same length.