What does the word "geopolitics" mean ?

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.