In his “Go Dojo” software Bruce Wilcox refers to this shape as an edge-crush: a third-line stone surrounded with the shape White has here is a sure kill however…
the crushing stones must have enough liberties during the ensuing fight
If the White stones cannot handle Black’s efforts to fight back then the edge-crush does not work. We will discuss a bit about that later
In the happy path Black is doomed
In the main line of play, Black nobi and White nobi lead to this formation and Black only has 2 liberties and no further threats.
In the unhappy path Black thwarts the edge crush
In this case, the edge-crush does not work because the “1” group has 2 liberties and Black has 2 liberties and it is Black’s turn to play.
In this example the edge-crush does not work because the cut at D1 kills stone 2 before Black will die.
Between the happy and unhappy paths lies the ko
I’m currently playing a correspondence game where me and the opponent have been battling back and forth over a ko or 5 or 6 moves. So even if the edge-crush does not lead directly to the happy path, you might play a few moves of the edge-crush during a ko situation as a threat.