The yarns showcased here are generally classified as lace weight. Lace weight yarns are very thin and, as the name implies, are most often used to create an elegant, lacy fabric with a lot of drape.
Remember that some yarns don't fall neatly into a category, so some categorized as slightly smaller or slightly larger may also meet your needs! Want more information about yarn weights? Check out this page from the Craft Yarn Council!