Final answer:
A trendline is a line added to a graph that shows the general direction of data points over time. It visually represents the trend of variables, such as unemployment rates, displayed in a line graph.
Step-by-step explanation:
A trendline is a line that uses current data to display the progress or general direction of the data. In a line graph, which is often used to show trends over a given period, a trendline can provide a visual representation of the relationship between two variables. One is usually measured on the horizontal axis, often representing time, and the other is displayed on the vertical axis, representing another variable such as unemployment rates.
For example, a time series line graph may illustrate how the unemployment rate has changed over time by plotting the points for each year's unemployment rate against time on the horizontal axis. A trendline added to this graph would help to clearly indicate whether the general trend of unemployment rates is increasing or decreasing over the observed time period.