Wiktionary
closest point of approach
n. (context nautical navigation English) An estimated point in which the distance between two objects, of which at least one is in motion, will reach its minimum value; abbreviated CPA. The estimate is used to evaluate the risk of a collision of e.g. two ships.
Usage examples of "closest point of approach".
The Navy called it CPA, Closest Point of Approach, the nearest distance that a straight course took you to another ship or point of land.
Kalgash Two is at its closest point of approach to Kalgash and ~ there's only one sun in the sky.
The floater passed its closest point of approach and she turned off her helmet lamp, then followed after it.