This shape is an empty triangle, empty referring to the unoccupied point at . Most people like to say that the empty triangle is bad, being inefficient and prone to shortage of liberties.
In contrast, the full triangle, with a White stone at , is good shape. This does not stop the existence of it being the best move on the board in some situations - good empty triangle.
is a hane on the second line. Black may fear what happens if he blocks. In the left diagram he creates an empty triangle. Things get worse with , wrapping around it and reducing the liberties to 3. In the right diagram, forces to connect and creates good shape with three in a row.
Elsewhere on the web
- Guo Juan's AudioGoLessons has three audiolectures on empty triangles.
- Empty Triangle is also the name of a Go comic strip.