MT 'aboda zara 11:10: "Who should be considered an enchanter? The one that cast spells [or pronounces words] that have nor meaning in a regular language, nor any intrinsic content, and he imagines that these [magic] words will have some effects [or powers]".
A spell, charm or incantation is a set of unintelligible words or a formula used to invoke some magical effects. Magicians, heathen priests and wizards in the ancient pagan world would use spells to cure, to protect and to harm (remember Maleficent and the Sleeping Beauty?) .
Casting spells was such a popular practice that you could hardly find the performance of any act of magic which would not involve the use of incantations. Magical speech was a ritual act of equal or even greater importance to the performance of non-verbal acts of magic. According to Bronisław Malinowski the pagans believed that "the knowledge of the right words... gives man a power over and above his own limited field of personal action."
The Tora calls the person who cast magic spells hober (see Deut. 18:11) and this practice is one of the idolatrous crimes forbidden by the Tora. Judaism believes that nothing could be achieved by magic or supernatural means. Everything is regulated by the will of God. For Maimonides the enchanters were mere charlatans who deceived people (specially people in despair!) giving them false hopes and unrealistic expectations.
One might think that in our modern world incantations, as well as all other sorts of idolatrous practices, are not as popular as they used to be. That might be true in many areas of life except for the best selling book series in the history of humankind: "Harry Potter". In Harry Potter, a children book, virtually all protagonists use spells, usually with the help of a magic wand, to acquire some sorts of superpowers. As we explain, the performance of magical spells and other procedures was seeing by our Tora and our Prophets (see for example Eze. Ch. 13) as a distinctive sign of godlessness. From this point of view, Harry Potter might be a good educational tool for us and our children to illustrate, in an ingenuous background, the ideas and beliefs of ancient pagans, against which Judaism fought for centuries.