Thumbs Up Icon: Just like Thumbs Up Clipart / emoji this icon is used to express approval / accepting someone’s argument or liking someone view in an argument. Thumbs up icon is normally used in web & mobile devices. Facebook thumb up icon is one of the most famous icon which become universal symbol/icon for social media popularity.
According to wikipedia
A thumbs up icon, usually described as a thumbs-up or thumbs-down, is a common hand gesture achieved by a closed fist held with the thumb extended upward or downward in approval or disapproval, respectively. These gestures have become metaphors in English: “The audience gave the movie the thumbs-up” means that the audience approved of the movie, regardless of whether the gesture was actually made. The term itself is an Anglo-Saxon word indicating the measure of a clenched hand with the thumb extended.