Witch cats of course refer to felines kept by Witches, or familiars. However, in the context of most of the articles here on PaganPath, Witch Cats usually refer to shadows seen out of the corner of the eye.
For more information, see the articles on the site:
<a href='http://paganpath.com/library-2/the-cauldron/135-witch-cats'>Seeing Shadows & Witch Cats</a>
<a href='http://paganpath.com/library/spells/129-attacks'>Handling Magick & Psychic Attacks</a>