In Zen Buddhism, ensō is a circle that is hand-drawn in one or two uninhibited brushstrokes to express a moment when the mind is free to let the body create.
It is rather like the brushstrokes of Japanese calligraphy or the Reiki symbols.
The ensō symbolizes absolute enlightenment, strength, elegance, the universe, and mu (the void).

The circle may be open or closed. If the circle is incomplete, this allows for movement and development as well as the perfection of all things. Zen practitioners relate the idea to wabi-sabi, the beauty of imperfection. When the circle is closed, it represents perfection.
The act of drawing ensō is a spiritual one, much like the sacred act of drawing the Reiki 2 symbols.

When drawn according to the sōsho style of Japanese calligraphy, the brushstroke is especially swift. Once the ensō is drawn, one does not change it.

The act of drawing a Reiki symbol focuses the energies represented by the symbol and its purpose is to change the energy surrounding it. In contrast, drawing ensō captures the character of its creator and the context of its creation in a brief, continuous period of time.

For me, it represents the circle of life, perfectly imperfect, just as it is.