explain parallax

[Jack]

Practically? Won't effect a shot on an antelope at all.
A parallax error at 300 yards won't be more than an inch or two. It's the least of your worries, in field shooting.
On targets from a bench, or varmints from a soid rest, where a 1 inch error in point of impact might be critical, parallax error could be a factor.
That's why scopes likely to be used for target or varmint have parallax correction, and typical big game scopes don't.
Worry about finding the exact range, getting a good position to shoot from, wind drift, trajectory, global warming, rattlesnakes, and Al Qeida terrorists before you worry about parallax while game hunting.