The triangle means an aspect of ki stream.

The circle is an universal emblem of infinity, perfection and eternity. The nature is shown in circles, rotations, and spirals. The circle is a zero, the emptiness realizing all these things. It represents a liquid aspect.

The square is steady, ordered and material. It is the basis of the physical world, which consists of the ground, water, fire and air. The square designates a firm aspect.

The Triangle represents the generating of energy and the initiative. It is the steadiest physical position. The circle symbolizes association, clearness and perfection. It is a source of boundless techniks. The square means the form and hardness - a basis of the control applied.

" The circle, a triangle and a square " can be interpreted at many levels, but for students of Aikido, the most suitable explanation of it is the association of heavens (circle), the human (triangle) and the grounds (square).