When you do your Captain certificates, you’ll be taught how to calculate Course To Steer (CTS) or the Heading you’ll need so your course over the ground will actually go where you want to go.
As you point in one direction and sail, you’ll slide sideways because of windage, tide and other forces that create leeway (sideways movement). This means, where you are heading is not where you’ll be sailing.
Modern MFD’s can display a line on your chart plotter for your heading, but also one for your “predicted” Course Over Ground (COG) where you’ll actually be going. This is calculated by your position, speed, wind etc. to estimate your COG continuously.
Because it is a continuous calculation it tends to be a very accurate representation of where your boat is actually going to pass in the water.