Oracle cards are any deck of illustrated cards used for divination, reflection or guidance that does not follow the fixed 78-card structure of the Tarot. The term "oracle" simply means a means of receiving guidance — and oracle decks can take almost any form: animals, angels, goddesses, plants, runes, affirmations, archetypes or purely abstract imagery.
The oracle card tradition is ancient in spirit if not in form. Cartomancy — reading meaning into drawn cards — appears in European records from the 15th century. But the modern oracle deck as a distinct genre, clearly differentiated from Tarot, emerged primarily in the late 20th and early 21st centuries, driven by the New Age movement's appetite for accessible, personal and visually diverse divination tools.
What distinguishes an oracle deck is the freedom of its creator. Unlike Tarot, which has a defined structure that all decks follow (22 Major Arcana, 56 Minor Arcana in four suits), an oracle deck can have any number of cards, any theme, any symbolic vocabulary. This freedom is both its greatest strength and its greatest weakness.