It was a system of magic discovered primarily by John Dee and his assistant Edward Kelley. Kelley received visions through a crystal, and John Dee generally organized it all if I'm not mistaken. Through various divination methods they believed that they communed with angels, and thus were given what they believed to be a variation of the Book of Enoch, provided in the language of the Angels - this the alphabet and language that they utilized, and the name of the magical system (Enochian magic).
There are several Enochian seals, utilized within the conjuration of Angels for further study and understanding of the Enochian magical system and all that comes with it. Beyond this, there is also a variety of tables utilizing the language to great "magical squares" that are used to achieve various ends. These correspond with the 49 Enochian keys evidently tied to the "Gates of Wisdom."