noun
1. : a point at which a course of events or a situation undergoes a significant change of direction or character : climax , crisis
1858 marked the turning point in the resistance of science to the new ideas concerning man's antiquity — R.W.Murray
turning point in a disease
turning point in a tragedy
2. : a high or low point on a graph or plotted curve
3. : a point the height of which is determined before a differential leveling instrument is moved and which is used to determine the height of the instrument after the resetting