The Suit of Disks
The Disks represent the element of the
Earth, the world of Assiah, Nefesh in soul.
Assiah is the world of making, literally translated as 'action', the actual material area in which all things live and grow physically. It is the final ground that all the preceding worlds need to become real. Assiah is stable and predictable, though it would be dead without the warmth of the Fires of Atziluth, without the Waters of Briah and the Air of Yetzirah.
So the Disks stand for the material world, the human body, the 'animal soul' that rules a far bigger part of our being than we usually like to admit. It often can be watched that the Disks are disregarded, looked upon as 'material only', with Assiah taken as profane and Nefesh as 'primitive'. But where would be the beauty of a lily without the earth in which it grows? What is a lily, anyway?
On the elemental plane Disks go well with Cups and Wands but don't harmonize with Swords.
In most other decks the Disks are called 'Pentacles' or 'Coins', referring to their material meaning. Crowley preferred the name 'Disks', most likely to stress the relation to the earth (in old times the earth was taken as a disk).