This is one of those terms that has a different meaning in academia than it does in common usage.
In common usage, people tend to use this word interchangeably with "international politics." It is a word that refers to political issues that have to do with large areas of the globe all at once.
In academia, the word has a much more specific meaning. It refers to a school of thought in international relations that is very much concerned with geography (therefore the "geo" in "geopolitics"). Perhaps the most famous example of this was the theory propounded by Sir Halford Mackinder about 100 years ago. He postulated that whoever controlled Eastern Europe would control the world because of the geographical location of that region and its size relative to the rest of the world.