This article is from the Charmed FAQ, by Colin A. McGregor (email@example.com) with numerous contributions by others.
Here is a list of some of the beings that are seen in the show.
Book of Shadows Put together by many generations of Halliwell witches this
is a manual describing both a wide range of magic spells, magic potions,
plus previously encountered types of nasty creatures.
Dark Lighter See White Lighter.
Ghosts Spirits of the (normally) recently deceased.
Warlocks: One of the most common types of nasty in the Charmed universe.
Evil beings that kill witches in order to steal their powers. Warlocks are
answerable to other nastier powers.
White Lighters: Guardians of new good witches. A very small number of
humans are at death given the option of becoming a White Lighter. Are
supposed not get involved with, or be known as White Lighters to the
witch(es) they are keeping an eye on (though over the course of the show
we will see an exception to this). White Lighters do have magic powers
themselves (but how extensive their powers are is a question left
unanswered). There are also Dark Lighters who wish to see witches used for
Witches: Normally good practitioners of magic. Being a witch is passed
from generation to generation via the female line, but witches are not
necessarily female (in season one we do meet one good male witch). The
appearance of magical abilities is normally seen when a person is quite
young, but can be suppressed until later in life.