The circle, triangle and square are symbols that you will find are very predominate in aikido.
You will find in certain organizations some (or a lot) of talk about "Ki." Whichever philosophy you subscribe to, if you will think of ki as the flow of physical energy... then associate that with those symbols, it will make some sense. Example:
Your basic stance in aikido is called "hanmi". Now, if you imagine yourself standing in a box, your feet will be in the two opposite corners of that box. (i.e. back right corner and upper left corner of the imaginary box. NOW... the o t h e r two corners are your weak points Start leaning in one of those directions and you'll find yourself falling over. Certain techniques will exploit those corners.
Hand movements will usually move in circular motions... hence the circle. It can be in just about any direction but there will be a cirlcle there.
Same thing with triangle: foot patterns will move in that fashion in the shape of a triangle.
Personally, I HIGHLY recommend the book "Aikido and the Dynamic Sphere." There are a lot of good explainations and diagrams for aikido moves in there. Some people don't care for it, but I liked it and keep it handy when I'm reviewing tests coming up.
And again... this is one of those things that you'll come to see in time. Circles, Squares and Triangles are all throughout aikido techniques if you look for them. If they (
) have any OTHER signifcance than this... it's new to me! (and that's entirely possible
Have a good day!