Hi
I'm looking at a Swarovski and the description says "reticles in the second image plane". What does this mean?

here's a link to us optics explanation of the two focal planes.

http://www.usoptics.com/sub_pages/reticles.php

If it’s a variable scope then the reticle will stay the same size (to your eye) while the target gets larger or smaller as you change the magnification.

A reticule in the 1st plane will increase or decrease in size along with the target as you change magnification.

The latter is handiest when using a ballistic type reticule since the relationship of the reticule and the target remains constant no matter what magnification you have set on the scope.