In Futures Studies, a trend is a time sequence of related events which indicate a general development or change in a situation or in the way that people are behaving. Some, but relatively few, are quantifiable and therefore statistically measurable.
Trends can be used to generate forecasts. The most popular way to do this is to extraplote the trend into the future, making the assumption that the trend will continue unabated. A more robust forecast can be generated by entertaining the reverse assumption and looking for other conflicting trends or possible surprises, often called wildcards, which might affect the trend's progress.
For example, academic libraries are starting to open adjoined cyber cafes. One might anticipate that the number of such cafes would continue to increase, since the idea of cybercafes is naturally popular with students. But any sudden decrease in funding for universities might serve to dampen or even reverse the trend. Also another large terrorist attack might erode the atmosphere of Internet and academic freedom on which cybercafes thrive. Worse yet, the government could suddenly close all such cafes in the name of homeland security. A variety of possibilities like these should be included in a forecast based on a trend.