Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Interactive fiction, often abbreviated IF, describes software simulating environments in which players use text commands to control characters and influence the environment. Works in this form can be understood as literary narratives and as video games. In common usage, the term refers to text adventures, a type of adventure game where the entire interface is text only. The term is sometimes used to encompass the entirety of the medium, but is also sometimes used to distinguish games produced by the interactive fiction community from those created by games companies.[citation needed] It can also be used to distinguish the more modern style of such works, focusing on narrative and not necessarily falling into the adventure game genre at all, from the more traditional focus on puzzles. More expansive definitions of interactive fiction may refer to all adventure games, including wholly graphical adventures such as Myst. As a commercial product, interactive fiction reached its peak in popularity from 1979-1986, as a dominant software product marketed for home computers.