Collection

A collection groups skins that were released together around a specific theme, operation, or map update. Most collections have a matching case that draws exclusively from that collection's pool, though some skins can also drop directly as an end-of-match reward without ever needing a case opened.

Collection is the organizing unit marketplaces and the in-game inventory use for browsing — "shop by collection" is usually how a player looking for a specific era or aesthetic of skins narrows things down, separate from filtering by weapon or rarity.