A word used when there is a hole in a wall, usually in a video game, where the character/person must make it through a small hole that may seem rather hard to fit in. The image is then saved and uses as a thumbnail on YouTube videos.
A thumbnail betrayal occurs on social networking sites such as facebook (the application 'are you interested' for example) when a male or female look really hot in their display picture, so u click thinking 'hell yea this is sweet' only to find out that they must have used some sort of magic 'grotesque removing' camera to take that picture with because they are, in fact, like a pile of shit which has been puked on. . attached to a bean bag chair. . with hair. .
dude: sweet this girl is hot *clicks*
dude 2: yea she looks sweet, look at her other photos
dude: omg ewwwww that was a pure thumbnail betrayal!! *gips*
When someone on an online dating site looks attractive in the list, but when you click to view their profile and see a larger image, you realize they're actually not attractive at all.
1 - Look at Joe's bleeding thumbnail!
2 - Jane quickly wrote a thumbnail summary of the chapter she had read.
3 - Bob drew a thumbnail sketch of his idea before he started his actual picture.