what is the name of the circle on spellcaster's feet?

Answer 1

Magic circle
In many branches of Ritual magic, and particularly in Wicca and other neopagan traditions, there exists a practice known as casting a circle or "circle casting". In modern witchcraft circle casting is generally done with salt, crystals, candles or other purifying materials, and requires special rituals to be considered effective.
By tracing a circle the practitioner consecrates an area within it for either temporary or permanent protection. This circle affords those within it to carry out magical rituals or spells without interference. Some traditions will say that one must go around the circle deosil three times: once to cleanse the circle with salt, a second time to cleanse it with water, and a third time to cleanse the circle with incense.
The most common set-up for a Wiccan circle would be with four (4) candles, one at each cardinal direction:
* North: green for the element of Earth
* East: yellow for the element of Air
* South: red for the element of Fire
* West: blue for the element of Water

Answer 2

Excellent Answer Irene.