In WordPress, a Thumbnail is a smaller version of an image that is used as a preview or representation of the full-sized image. Thumbnails are often used in WordPress to display images in a more compact form, such as in a gallery or on a post or page.
Post thumbnail was introduced in WordPress with Version 2.9. This feature is currently known as Featured image.
WordPress automatically generates Thumbnails for images that are uploaded to the media library, and you can choose to display the Thumbnail size for images in various places on your website.
The size of a Thumbnail can be customized in the WordPress settings, or you can create custom Thumbnail sizes using plugins or theme functions.
Thumbnails can also be used as a featured image in WordPress, which is a specific image that represents the content of a post or page. Featured images are often displayed in search results, archive pages, and other places where a quick preview of the content is needed.
Overall, Thumbnails are a useful tool for displaying images on your WordPress website in a more compact and visually appealing way.