from textiles.com: Definition of muslin: Cotton sheeting fabric with thread count of less than 180 threads per square inch.
An inexpensive, medium weight, plain weave, low count (less than 160 threads per square inch) cotton sheeting fabric. In its unfinished form, it is commonly used in fashion design to make trial garments for preliminary fit.
A large group of plain weave cotton or cotton blend fabrics. They cover a variety of weights from light, fine sheers to heavier sheetings. Used in interfacings, dresses, shirts, sheets, furniture covers, and many other applications.
Muslin is a type of finely-woven cotton fabric, introduced to Europe from the Middle East in the 17th century. It was named for the city where it was first made, Mosul in what is now Iraq.
A thin cotton, white, dyed, or printed. The name is also applied to coarser and heavier cotton goods; as, shirting and sheeting muslins.
Muslin, named for Mosul, a textile center in ancient Mesopotamia (modern Iraq), is now a generic term for a simple-weave fabric ranging from sheer to heavy sheetings. Fine muslin is smooth, with a 180- to 200-thread count.
Kind of interesting!