Divinations was the skill which governed the casting of Divinations spells. Improving this skill increased the spell power of these spells as a well as the chance of casting them successfully.
Divinations focused on knowledge and detection. Many spells like Detect Curse and Magic Mapping were replicated from scroll effects. Ashenzari, the god of Divinations (introduced after this school's removal), filled in the other gaps.
For a long time, while the Divinations school was unavailable to players, its miscast effects were used for a few aspects of the game.