Muslin is a light cotton fabric, finely woven and typically white, that was first imported from the Middle East to Europe in the 17th century. It is named after Mosul in modern-day Iraq, the city through which it made its way to Europe, but Dhaka in modern-day Bangladesh is the fabric's true place of origin. Muslin is a popular choice for clothing and curtains, particularly in hot, dry climates. It may also be used as padding for furniture.

Muslin has many uses besides those listed above. Because it is a relatively cheap fabric, it is not always used for clothing or upholstery, as more expensive fabrics often are. In sewing, muslin is often used to make a test garment before sewing with expensive fabric. This practice is so widespread that a test garment made with synthetic fabric is also referred to as "a muslin."

Muslin can be used to filter wine of impurities during the decanting process. A funnel with muslin stretched over the narrow end may be used to transfer wine or port into a decanter, keeping any sediment out.

Muslin is used widely in the theater, where it is very versatile. Myriad staging effects can be created with muslin, as it can be painted with any scene you can imagine, hung straight or draped, and even treated to appear semi-translucent, similar to a scrim. Being lightweight and inexpensive are significant assets for a fabric used in set design.

In addition to the stage, muslin is useful in television and film. When painted in a uniform color, the fabric can be used as an inexpensive greenscreen. Muslin may be bought pre-colored for this purpose, but it is also relatively easy to prepare oneself with diluted latex paint.

The word muslin may not always refer to the cotton fabric described above. In Britain, any gauzy cotton fabric may go by the name of muslin, while in the United States, muslin may be any firm, sturdy, inexpensive cloth. In nautical slang, a ship's sails are referred to as muslin.