When a goalie comes out of his crease toward an oncoming offensive player to limit the amount of space in the net the shooter is able to aim for.
Simple physics shows why the technique of "Cutting down the angle" works so well for goaltenders. However, the risk is coming out too far and opening up a wide open net if the offensive player can read what the goalie is doing and either fake a shot or pass it to teammate for the easy tap-in.
In the last 20 years, goalies have perfected "Cutting down the angle" and use their size and positioning to do more controlled puck-stopping moves. Before the 1990s, many goalies used what was known as the "stand-up style" and attempted to rush out at offensive players to cut down the angle and force them to shoot. Patrick Roy is credited by many for the change in philosiphy and the fundamentals of "Cutting down the angle."
One of the most famous plays where a goalie was burned trying to cut down the angle was when Daryl Sittler took Don Cherry's advice in the 1976 Canada Cup to fake a shot if he went in on goal. Cherry asserted Czechoslavakia goaltender Vladimir Dzurilla was over-committing to cut down the angle, and sure enough, Sitler faked, and sailed home the tournament-clinching goal.