A witch is someone who pretends they can impact the world through spells, symbolic magic, or potions. In reality they only impact their own social standing.
In the Middle Ages loads of people were accused of being witches. The main reasons for the accusations were that the victim was 1) powerless 2) a burden on the community 3) prone to pissing off other people 4) ugly.
If you were accused of being a witch you were going to be tortured then either killed or force to leave your homeland. The whole thing kind of blown over when people were no longer retardedly interested in superstition. Most famously an English judge ruled in a case where a woman was accused of flying over the village. The judge (the first non-retarded judge in England, possibly the last) ruled she was innocent as there was no law banning flying in the village. Sometimes if people can't be reasoned with you have to stoop to their level to get through to them. We call this the "internet arguement" principal.
Nowadays people pretend their witches in an attempt to make themselves seem interesting. Also if witchcraft was real we're pretty sure there would be a LOT more hot witches out there. As is, it is only every now and then you will find that diamond in the rough that is actually a very, very hot witch (or goth or wicca or whatever they want to be called).
Only she could convert us to witchcraft.