A Witch is a practicioner of the religion/craft of Wicca. Wicca as
it is practiced today is a religion which draws upon certain ideas
which predate Christianity, but also draws on modern thinking as
well. It is often refered to as a neo-pagan religion, since it is
generally a reconstruction and/or modification of some ancient
beliefs.

There are hundreds of different branches of Wicca, each with its
own beliefs, central ideas, area of importance, ideals, etc.
Anyone can create their own new branch of Wicca if their beliefs
dont quite match up with that of an established coven - most
practicioners do not see their way as being the ONLY way (I
certainly dont - religion is a personal thing, and no two persons
are the same...).  There are a number of common beleifs and views,
of which few, some, most, or all may be shared by any given coven.

1.  The existance of a supreme entity/entities - often considered
    benevolent, though sometimes neutral.
2.  The supreme entitiy/s are often divided into both male and
    female aspects.  Some covens only recognize one gender,
    however (usually the Goddess aspect)
3.  The practicioners honer these deities on certain occasions,
    sometimes refered to as Sabbats and/or Esbats.
4.  These gods/goddess may have one or several names, one or
    several aspects.
5.  The practitioners recognize the existance of a power that
    exists all about us, and are often trained in how to recognize
    and manipulate such energies to various effects.
6.  Most (if not all...) true covens adhere to a particualar creed
    - 'So long as it harms noone, not even yourself, do what you
    will'. There are many variences to the wording and intent.
7.  Practitioners may be trained in how to understand certain
    symbological figures that affect both their craft work and
    their daily lives.
8.  The number of members in a coven may vary from one to twelve
    or thirteen, or perhaps even higher - as a general rule,
    though, it often is a very small, private, personal religion.
9.  Many covens have a heirarchy of degrees, the lowest generally
    being an 'initiate' or 'novice', the highest being a 'high
    priest' or 'high priestess'. There may be 3 levels, or more. A
    person who is recognized as being a 'priest' in one coven may
    or may not be necessarily recognized within another. The
    degrees usually reflect the amount of training a person has
    within his own particualr coven and in the religion in
    general.
10. Many covens do not recognize the existance of a supreme entity
    of evil - there is no 'Satan' as it is for most all members.
    Satanists and witches are COMPLETELY seperate fields (in fact,
    not all Satanists beleive in a supremem entity of evil
    either...).

I could go on, but that covers a lot of basic ground. As you can
see, I've purposely tried to leave out absolutes, because the
religion is so unique to each person and group. I've been taught
to recognize most all branches of Wicca, known and unknown, and I
hope my definition is somewhat fitting (if somewhat vague!)
                             Silvernote
