A sliver (rhymes with diver) is a long bundle of fiber that is generally used to spin yarn. A sliver is created by carding or combing the fibre, which is then drawn into long strips where the fibre is parallel.  When sliver is drawn further and given a slight twist, it becomes roving. 
- Yarn Production, National Cotton Council of America
- Freund, Kimberlie and Norton, Marjorie J.T., Broadwoven Fabrics, USITC Publication 3410: 4 ISBN 1-4289-5826-6
- Spinning Prep/Combing Lab, International Textile Center
"gilling". Australian Wool Testing Authority. Retrieved 2019-06-11.
Gilling is the blending together of card slivers with the direction of feed alternated to make a final sliver suitable for spinning.
"Manufacturing of Worsted Yarns:". textile learner. Retrieved 2019-06-11.
The preparative gilling is mainly to align the fibers in a parallel direction, further blend the wool through doubling and to add moisture and lubricants.
"WORSTED - TOP-MAKING". Woolmark. Retrieved 2019-06-11.
The latter is achieved by passing the wool at least once through a special gilling machine which has an auto-levelling device, which continuously detects the linear weight of the slivers being fed into the machine, and speeds up or slows down the machine accordingly.