A trend is an inclination in a particular direction.  

For water quality and air quality indicators, any long-term trends often take several years to be detected because of the wide variation in measurements that occur from day to day or among seasons.  Where there are enough data to calculate a trend result, LAWA shows this as improving, no measurable change (indeterminate) or declining (degrading). View a factsheet on calculating water trend.

For land cover, you can see how the different land cover classes (e.g. forest) may be increasing, showing no change, or decreasing in area over time.  See the factsheet on calculating land cover trend.