I see lots of people still equating the heading from some sort of compass, with the course from a GPS. This and another thread got started because the two are different, and it can be an important difference.
I think most of the confusion is because on land, whether walking or driving, course and heading will always be the same because you don't "slip" on the ground as you walk or drive - at least not under any normal conditions.
In contrast, on the water and in the air, cross winds, cross current, etc can be pushing the boat sideways while at the same time you are steering and propelling the boat by it's motor. Your actual geographic track is a combination of the two.
In a boat, and using boat terminology, The direction that you are steering your boat, which is the same thing as the direction the boat is pointing, is the Heading, and is measured by a compass of some sort that is fixed to the boat. A GPS (excluding sat compasses) is not able to measure that, at all, under any circumstances.
The progress that a boat makes, geographically, is it's course, or more precisely Couse Over Ground (COG). This is what a GPS measures, by noting successive geographic locations, and "drawing" lines between them. Is the same way that a GPS can't measure heading, a compass can't measure COG. So these are different and complementary devices.
As an aside, when I say "GPS", I don't mean a chart plotter. I mean the GPS device that listens to the sats and reports lat/lon, COG, SOG. That might be stand-alone, or it might be built into your chart plotter.
Now in many cases people simply ignore the difference between HDG and COG, and make whatever steering corrections are required to get where they want to go, and that's absolutely fine. And that's because under lots of situations, probably the majority of situations, COG and HDG are the same or very close since there is very little cross current or cross wind, and of course this encourages people to simple equate the two.
But regardless of how much you distinguish between HDG and COG when operating your boat, it can't hurt to understand the difference, especially when you find you boat pointing 20 degrees off from where your chart plotter says you are going...And the difference really matters a lot if you want to have a better understanding of your nav electronics and what each component does, and why it's important.