A thumbnails is usually a box with an images, used to show a short preview of a post, page, product and etc. When it is clicked, a new page or a popup is openThumbnails are used to list posts, products, videos and different sides of a web site. They are usually consist of an image combined with a text. Various effects are available for the thumbnails to make them more interesting. See below.ed to show more details about the selected topic.