It's the pattern the lines make with the ambient magic, anywhere in the world but here.

Aurora's circle could cut me off from drawing upon ambient magic to fuel a spell-but it couldn't stop me from using the energy within me.

It, too, varies with the ambient magic, but it is always by far the strongest on the surface of Xanth.

Our wares are very sensitive to changes in ambient magic; something we might not notice could cause them to go wrong.

He would, if the ambient magic in Highjorune wasn't going to mask my relatively weak spells.

Magic-sniffers who can see and identify ambient magic aren't common, but the Mages' Society keeps a list of those who can do it.

She has ambient magic with metal and fire.

He liked the ambient magic of Xanth.

Her ambient magic consists of metal and fire.

All four have ambient magic, as opposed to academic magic, and the power they use comes from ordinary things all around them.