Enso is a Japanese word meaning “circle” and a concept strongly associated with Zen. It symbolizes enlightenment, strength, elegance, the universe, and the void. In Zen Buddhist painting, enso symbolizes a moment when the mind is free to simply let the the body/spirit create.
Some artists may paint enso with an opening, which may express various ideas. For example, it may express that imperfection is an essential and inherent aspect of existence. This is the core aspect of the Japenese aesthetic: Fukinsei — the denial of perfection.