An emoji is a small image, either static or animated, that represents a facial expression, an entity or a concept (among other possibilities) in digital communications.
The emoji is the graphical successor to the emoticon, which represented similar things through sequences of characters, such as :) to stand for a smiley face. Depending on the application, an emoji may be inserted simply by clicking the desired image or converted from text characters. Emoji collections are widely available on social networking sites, smartphone apps and other messaging platforms.
The word emoji is made up of Japanese words meaning picture (e) and character (moji). The first emoji were created by Shigetaka Kurita, who borrowed the idea from weather forecasts that used symbols, Japanese characters, street signs and manga, a style of Japanese comic that -- like Western cartoons -- uses a standard group of symbols to express emotions and concepts. The Japanese telecommunications companies NTT DoCoMo, au and Vodafone (now SoftBank Mobile) each created their own proprietary collections of emoji.
As the number of emoji has increased, the meanings of many have become more open to interpretation. While basic emoji like the smiley or winky faces are generally understood in the same way by most viewers, an image of a man with blue triangles over his head or one with two open hands touching at the wrist and facing forward might be interpreted in a number of ways (Their official meanings, however, are "man bowing" and "whatever.").
See an emoji-supported video on the history of the emoji: