A trend line in a scatterplot can be used to make predictions in real-world situations by seeing the trend within the plot. Seeing a trend line that can be positive, negative, or none can help predict what will happen next. A trend line describes how the variables are related, made up of points where for a given x-value, there is a prediction for a y-value. And the points that make up the trend line is consistent with the relationship between the two variables.