Resources in TiddlyWeb are divided into entities, singular resources, and collections, aggregations of entities. For example a tiddler is an entity and what you get when you go to https://tank.peermore.com/bags/tweb-filters/tiddlers is a collection of tiddlers.
Some collections are aggregations of other collections. The recipe process in TiddlyWeb aggregates one or more bags, gathering tiddlers from each, creating a collection of tiddlers which are the recipe's tiddlers.
In a recipe each bag may be filtered, and then the resulting recipe's tiddlers may be filtered as well.