The Schools of Magic (PHB)

Spells are divided into nine different categories, or schools, according to the types of magical energy they utilize. Each school has its own special methods and practices.
Although they are called schools, schools of magic are not organized places where a person goes to study. The word "school" identifies a magical discipline. A school is an approach to magic and spellcasting that emphasizes a particular sort of spell. Practitioners of a school of magic may set up a magical university to teach their methods to beginners, but this is not necessary. Many powerful wizards learned their craft studying under reclusive masters in distant lands.
The nine schools of magic are Abjuration, Alteration, Conjuration/Summoning, Enchantment/Charm, Greater Divination, Illusion, Invocation/Evocation, Necromancy, and Lesser Divination.
This diagram illustrates the schools that oppose each other. See Table 22 and its entry descriptions for more information.
Of these schools, eight are greater schools while the ninth, lesser divination, is a minor school. The minor school of lesser divination includes all divination spells of the 4th spell level or less (available to all wizards). Greater divinations are those divination spells of the 5th spell or higher.