Once used only by geeks sending text messages to each other, they are now immensely popular. Some now claim that emoji may be the fastest-spreading language on the internet. The BBC, a British broadcaster, has started to summarise its weekly news using strings of emoji to reach a younger audience, and classic novels such as Moby Dick are now being translated into the icons. But the little pictures that make up emoji are confusing for many. So what are they and what do they actually mean?

Emoji (Japanese for “picture-character”) are smiley-face icons that users of computers and smartphones send to each other to convey meaning or emotion. Although they have only become popular recently, the use of typeface to create graphic art dates from at least the "typewriter art" of the 1940s. But with the advent of the internet, emoji and their precursors, emoticons, evolved rapidly. The first use of graphic text on computers was the “:-)” emoticon, proposed in 1982 by a man who was frustrated by his colleagues’ inability to understand when he was making a joke.

Ready-made pictures for text messages were first included with Japanese smartphones, but when they started sending messages to the rest of the world, the pictures would be rendered incorrectly. Thus Unicode Consortium, a non-profit organisation, stepped in to make a set of standards for emoji, of which there are now 722. The Unicode Consortium built on the work of other standards-setting bodies, such as the American Standards Association, and extended the encoding of Roman characters to include accented letters, which were coming into use as the internet expanded into non-English-speaking countries.

Emoji are rendered differently under different fonts, of which the Apple Font used on Macs and iPhones is most ubiquitous. Yet in March the Unicode Consortium issued a new set of recommendations to font artists, such as “make the pouty face more pouty—not intended to depict anger”. Some of their suggestions tackle the fundamental problem of translation: to be understood precisely across different cultures. Emoji 1F62A, named by Unicode as “sleepy face”, is drawn with a bubble from the mouth, which represents sleep in Japanese cartoons, but is often interpreted in other countries as meaning crying or drooling. But removing the bubble will change the interpretation of the emoji in Japan, Unicode warned. The best way to understand the fluid meaning of emoji, then, is to consider their context. Or simply ask the author.