In the world of spinning, a batt is wadded blanket or sheet of fiber that has been prepared on a drum carder. You can see photos of the process at the Joy of Hand Spinning. The last of the three photos on their webpage shows a solid-colored batt being lifted from the drum carder.
While some batts are composed of solid-colored fiber, others have multiple colors blended together. The wildest of the multiple colored batts are referred to as art batts. I just bought my first one.
It had tons of wonderful colors, with a preponderance of lavender and turquoise. There were lovely textural nubs of wool, pieces of metallic, and other lovely bits to wind up in the yarn. My spinning process was more loosey-goosey than normal because I wanted a wild thick and thin ply.
Here are some other little bits that got spun into the art batt fiber: pieces of lace, tattered hunks of rayon fabric, strands of handspun yarn leftover from other projects, eyelash yarn, and more. The color tone of this batch of extras was most deep blues and royal purple.
Because I wanted to end up with a little more yarn than the batt would provide another ply of mostly a solid media aqua Merino was spun. This one was done with more evenness and about 10% of the original batt was held back to combine here and there.
The result was a fun skein of one-of-a-kind yarn: