shippou (pattern)
七宝 (shippou) or 七宝つなぎ (shippou tsunagi), lit. "seven treasures"
A traditional, Japanese pattern made up of overlapping circles. For a good example, see the backgrounds of post #660754 and post #1036201.
See also
- Saigyouji Yuyuko's fan design
- Tag Help - Traditional Japanese Patterns (Danbooru Forum Discussion Thread)