Two inclusions found within a diamond that have twisted together; inclusions capable of becoming a twinned wisp are crystals, pin points, needles, and clouds. These inclusions appear to the viewer as a white stripe within the diamond (under 10x magnification). Twinning wisps occur most often in fancy diamond shapes like the heart of the pear as those shapes are cut from rough that usually features twinned crystals; however they can and do occur in other diamond shapes.
See Also: Wisp, Feather, Fracture, Inclusion