I was reading a review for a camera lens. I found the sentence there.
Slow focus on my 300D, noticeably better on a 400D... Shallow focus field, with lots of hunting.
This is a photographic term for a behaviour of auto-focus.
When using auto-focus, the camera will make an estimate about where the right focus is based on the image that it sees through the lens, and adjust the lens to that point. Then it will make a new estimate and close in on the right focus in smaller and smaller steps.
If the camera misinterprets the image that it gets through the lens, it might move the focus point back and forth past the right focus several times, causing a characteristic ticking sound, and this behaviour is called hunting.
I interpret this to mean the lens user has to spend an excessive amount of time finding (or waiting for autofocus to find) the field of focus. Or in other words...
Lots of time spent hunting for the field of focus.