I have just recently had the privilege of obtaining a new rifle and scope. While the scope is no Swarvoski, it isn't a " cheap-o" either. It is actually the best that I have personally owned and used to date.
My question is this: What exactly is "parallax" and what is it effect, if any, in the real world when I am hunting those Wiley Coyotes? My scope has numbers etched into the steel at the "point tword target" end. Twisting the end, of course, moves the numbers about, adjusting them from 5 yards out to infinity.
Please tell me how to use this feature to my advantage. And no jokes please! Reading back over this post has made me feel like an idiot as it is! But I really want to know.
Thanks for your help.

Don't ask me about the technical details of what causes this - something about dimensions and tolerances around the erector tubes??

The practical effect, is that if you sight through a scope at a target distance where the scope is not parallax free, and you do not sight along the exact middle axis of the scope, your POI will diverge. A scope parallax free at a particular range will not see diverging POIs if you sight through the scope a bit differently from shot to shot (very hard to impossible to avoid).

Most scopes (for center fire rifles - e.g. intended for hunting) will be set to be parallax free at 100 yds (or meters - for European scopes). Scopes with adjustable parallax will allow you to adjust the target distance at which the scope will be parallax free.

This is most useful for scopes used for very small targets (e.g. target shooting, varmint hunting etc). For large(r) targets, the diverging POIs normally mean very little, and adjustable parallax just becomes one more (unnecessary) thing to fiddle with.

Some scopes seem to suffer very badly from parallax errors, and others seem a lot more forgiving. In the past, the higher end Leupold scopes have done well for me in this respect.

FWIW - mike

AS MHO says, a scope with a parallax adjustment will allow you to reduce potential aiming error due to parallax to zero for a given distance. I say "potential" because if your eye placement is identical shot-to-shot then there is no parallax error to begin with.

Adjustable parallax is only important in precision target shooting or when shooting at very small and distant varmints. In my opionion, which is reflected in the scopes I own, parallax adjustment on a rifle which is primarily a big game rifle is an unneeded complication which merely represents one more system which is subject to failure or moisture leakage (although it is true that most high-quality scopes have no problem with this, anyway.)

To illustrate how small potential parallax aiming error is, Leupold's non-adjustable (non-Rimfire) scopes are preset with parallax adjusted for 150 yards. The maximum aiming error -- if you place your eye at each extreme of the sight picture for two successive shots -- is only slightly more than one-inch at very close/very distant targets. Usually not enough to spare the life of a coyote, much less an elk.