Collections
Group your products. One product can belong to several collections at once.

Collections vs. categories
A category is what the product fundamentally is (skincare / household cleaning), and usually there's one per product. A collection is a marketing grouping (new arrivals, Mother's Day picks, selling fastest). A product can sit in several, and they come and go with your campaigns.
Question: Can a collection update itself?
Yes. Set conditions (a price range, a tag) and matching products join automatically, with nothing to maintain by hand.