What is a scatter chart ? How is it different from line chart ?

The scatter chart is a graph of plotted points on two axes that show the relationship between two sets of data. With a scatter plot, a mark or marker (usually a dot or small circle), represents a single data point. With one mark (point) for every data point a visual distribution of the data can be seen. Depending on how tightly the points cluster together, we may be able to discern a clear trend in the data.

The difference is that with a scatter plot, the decision is made from the data points such that the individual points should not be connected directly together with a line but, instead express a trend.