Witchcraft
The science of spell casting and healing.

Witch
Wise one...someone who is able to heal others and cast spells.

Wicca
A nature based religion that celebrates the Goddess and the God in any of their many guises.

Wiccan
Someone who believes in the Goddess and the God and practices witchcraft.

Pagan
Means country dweller.  Today used as a general term for followers of wicca & other religions.
 

Wicca...a further definition

A nature based religion, commonly referred to as witchcraft, in which the practitioners believe in
the Goddess and her consort, the God, as well as other divine entities, and perform rituals to celebrate the Divine creatures and the eight Sabbats and Esbats, invoking the spirits, elements, divine entities, etc. to help.  Wiccans choose form several traditions, such as Gardenerian, Traditional, Pictish, Eclectic, etc., based on the pattern or standards that fits them and their lifestyle the best. 
 

Witchcraft...
(This is the NEW WORLD DICTIONARY'S definition of witchcraft.)

Noun  1. a) the power or practices of witches; black magic; sorcery  b) an instance of this 
2. bewitching attraction or charm. 

They say to see the definition of magic and basically I go along with what the dictionary says aside from the fact of sorcery or black magic...my personal definition of witchcraft is this: the art of performing rituals and magick (with a "k" to distinguish it from magician's magic) and spells, most often with the aid of tools and the invocation of spirits.
 

On a further note...

The dictionary says that a witch is a person that practices black magic or a person supposedly having supernatural powers by a compact with the devil or evil spirts; a sorceress, or a male known as a warlock.

A lot of Wiccans don't like going by this definition and being called witches because of the way it
presents them.  I personally don't care because, one: I don't believe in the devil and two: another definition of witch is a bewitching or fascinating woman or girl and thats what I am (I hope!-lol!)

So it's not politically correct but it is just safer to call Wiccans just Wiccans or Pagans, unless they specify that the word witch doesn't bother them.
 

NOTE:  The two in-depth definitions of Wicca and Witchcraft and the information under "On a further note..." were graciously given to me by SilverRowan for use on this web site.  Thank you so much again.