A Basin of Attraction in which every point on the common boundary of that basin and another basin is also a boundary of a third basin. In other words, no matter how closely a boundary point is zoomed into, all three basins appear in the picture.
See also Basin of Attraction
Nusse, H. E. and Yorke, J. A. ``Basins of Attraction.'' Science 271, 1376-1380, 1996.