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 opened to show more details about the selected topic.
Image thumbnail splits on hover and the texts become visible.
A thumbnail with social sharing buttons and title box, which fades in and out on hover.
Thumbnail examples with various sizes and hover effect.
Thumbnail with effect on mouse hovering.
Responsive video thumbnail for Youtube with player.