Loose connection
From HexWiki
There are many different types of loose connections, two of which are described below.
Type I
The pieces on this board can be connected by a bridge by placing a red piece at either of the cells marked "*". These are the same places where Blue can play to try to prevent the connection.
Type II
This connection is a bit weaker than Type I.
Red threatens to connect the pieces by playing at one of the cells marked "*", which form two bridges between the original pieces.
The obvious way for the Blue to stop this connection is to play in one of the cells marked "+", which is where Red's threats overlap:
This is a reasonable defense because either of the two moves "+" will block potential bridge connections. Here is an example: