The hash for the Socket Category: a quick way to go get the header display information for the category. Use it to look up DestinySocketCategoryDefinition info.
Mapped to DestinySocketCategoryDefinition in the manifest.
Use these indexes to look up the sockets in the "sockets.socketEntries" property on the item definition. These are the indexes under the category, in game- rendered order.
Sockets are grouped into categories in the UI. These define which category and which sockets are under that category.