Circle of Power

A Magic Circle of one kind or another is used in most Magic. First mentioned in Storm Front.

Description
Circles create boundaries that isolate an area inside from the magical energies of the world outside.

A Circle helps a Wizard refine his magic, focus and direct it more clearly. It create a sort of screen, defined by a perimeter keeping random magical energy from going past it. It can be drawn on the ground or made by a several people holding hands, or a number of other methods. Then it's invested with a bit of energy to close the circuit.

Learning how to properly establish a circle is the first thing any apprentice is taught.

Notable Uses in the Series
In Storm Front, Harry traps Toot-toot in a circle to bribe him with bread, milk and honey in order to get information on Victor Sells.

In Turn Coat, Harry draws a circle around Murphy and himself when they are surrounded by Grey Suits. The repeatedly attempt to enter the circle by bumping up against it then by pressing their palms—which had mouths containing sharlklike teeth, purplish-black tongues, and yell mucus—against the circle. Seriously "Eckgh!". Then,  Molly Carpenter draws a circle around Binder's minions, the Grey Suits, at Morgan's suggestion, which cuts off the flow of energy they needed to maintain solid forms. They suddenly melted into transparent ectoplasmic gook.