A popular device used for quotation and storytelling.
This began on the *chan imageboards, where quoting text places a > in front of it, turning it green. This effect can also be done manually. Before long, this feature was put to innovative use. When quoting another post, greentext is frequently used for summary, criticism, and ridicule. Its other major use is storytelling, in which a lengthy story is told through fragmentary statements in greentext.
Greentext became highly popular for both of these functions due to its convenience. When quoting a post, it is easier to summarize than to respond in full. When telling a story, stringing together sentence fragments is a
grammatically easier
alternative to prose composition (it also makes for lighter reading).
This feature has become so widespread that it is sometimes used outside of imageboards (eg
Youtube comments).
