In the context of videos, a thumbnail refers to a small image or preview that is displayed to represent the video before it is played. Thumbnails typically appear as a still image or a short video clip and are displayed on video sharing platforms such as YouTube, Vimeo or TikTok. They are designed to give viewers a quick glimpse into the content of the video and to entice them to watch the full video. A good thumbnail can therefore be an important factor in attracting viewers and increasing the number of views for a video.

Thumbnails can also be used as design previews in the ideation and planning stages of a design project, allowing designers to quickly explore and iterate different ideas before committing to a final design.