(*third-person singular simple present* zeros in, *present participle* zeroing in, *simple past and past participle* zeroed in)

- zero in on

The phrase possibly comes from adjusting a sighting mechanism of a firearm to minimise the discrepancy between where the sight points and where a bullet lands on a target.

Another possible source is from the Cartesian coordinate system in mathematics. In the coordinate system, shapes are generally defined out of an origin (the generic point of reference) labeled O, with an x,y coordinate pair of 0,0.