Among the ultra sound patterns observed during examination are two frequently described as sludge and gravel.
Gravel is the appearance of multiple small stones that are reflect the ultra sound signal and cast a shadow.
Sludge also returns a signal but does not cast an acoustic shadow. It also is more viscous and does not move around the gallbladder as rapidly as gravel.
The ultra sound technician moves the sensor into different positions and often moves the person to see if the pattern is mobile, viscous, or static.
Chaff as far as I can remember was a phrase coined by someone on curezone to describe the small pieces of debris expelled during a liver flush. I haven't seen it mentioned in any medical papers.