In futurists' parlance, time horizon is the farthest distance in the future to be considered for the current study or project.
The time horizon is used along with the domain definition to determine the scope of a futures forecast or scenario planning exercise. For instance, an organization may be interested in exploring the future of medicine over a time horizon of ten years. Because the time horizon is just ten years, the client would not be interested in considering emerging medical technologies that are much over ten years from commercial application. A time horizon of fifty years would allow for a wider variety of intriguing future scenarios, but then the project may not be as useful to the client.
In choosing a time horizon for a project or forecast, consider the client's cycle time, or the time it takes the client to produce one unit of work. Weapons systems may take fifteen to twenty years to develop, so military clients need to look more than ten years into the future. A clothing designer, who has a considerably smaller cycle time with at most months needed to bring a new product from designs to market, would likely find a twenty year forecast too broad and diffuse to be very useful.