If a scatter plot shows a linear association, then there is a line that describes the relationship between the two measured quantities reasonably well. This means that there is a clear pattern in the data, and that the data points tend to follow a straight line when plotted on a graph. This does not necessarily mean that there is a line that passes through all of the plotted data points or that there is a tendency for relatively high values for one measured quantity to be paired with relatively high values for the other measured quantity.
