Witch refers to a female who can use magic. The male counterpart is a Warlock. Witches are known to live in Halloweentown, and now some have crossed over into the mortal realm after the portal opened.
Witches in Halloweentown seem to be normal, while they were formerly reviled in the mortal realm and driven out like other creatures. In fact, a former queen of Halloweentown, Splendora Cromwell, was a witch. Many years later, Cromwell Castle became a college for witches and warlocks and operated as such until Marnie Piper opened the portal between Halloweentown and the mortal world.
Witches can cast magic, make potions, and ride brooms. It is typical for a witch to start her training once she turns thirteen. Beforehand, witches can still ride brooms and will continue to do so into and after their training. Witches use spells written down in spellbooks, and may keep an array of potion ingredients.
It is possible to take magic away from witches through certain spells. Witches can also be put into a Witch's Glass, which is powerful enough to keep them captive inside the mirror.