Witchcraft is a practice of magic especially black magic the use of spells and the invocation of spirits.
In the book
The Crucible AbigaIl and Tituba are accused of witchcraft because they were dancing naked around a cauldron and Rev. Parris saw them but didn't tell. Betty got sick and everyone thinks Tituba is the witch and Abby starts pointing the finger at other people that's how this book starts.
I think that Abby is the witch because she is trying to blame other people to make it so that Jon Proctor's wife is out of the picture.