The key concept of territory can be understood in various ways:
- Superficially speaking, territory is the empty points surrounded, or rather "controlled", by a player.
- To specify what control means, we can say that territory is a part of the board that is surrounded by stones belonging to a living group, and in which the opponent cannot make a living group
This black group delimits two areas, in which he will easily make an eye. The group is clearly alive. It is impossible for White to create a living group with two eyes in the area. Black makes 21 points of territory.
The term territory is used in various ways when discussing a game of Go.
- Definite territory, like it is defined above, mostly when it is counted at the end of the game
- Estimated territory, during the game, when a position is sure to yield territory, but the exact amount is not yet known
- Potential territory, during the game, when a position is likely to yield territory, but can still be invaded
- The existence of territory necessarily means that the surrounding group has a base. Obviously, this base is often to be found where the territory is. Therefore, territory sometimes conceptually interferes with base or eyespace.
The circle-marked points constitute an area controlled by White, where Black can't make a living group (if White answers correctly). We can say that this 3-3 invasion makes roughly 10 points of territory.
 Assuming normal play.