A selvage, or selvedge, is a type of edge on a piece of fabric that prevents individual stitches from unraveling or fraying. The term is derived from the phrase "self-edge," because the formation of a selvage is a natural result of how the fabric is made. Historically, selvages were only found on woven fabric, but in modern times the term has also come to apply to self-finishing edges on knitted fabric. In both weaving and knitting, these finished edges help to create seams that are evenly aligned.
Creating a selvage in woven fabric is usually accomplished by securing horizontal weft threads along the side edges of the fabric. This can be done by reversing the direction of the weft threads at the end of each row of weaving, and then wrapping the threads under and over the vertical warp threads that run lengthwise through the fabric. The type of thread and weave used to make selvages may be the same or different from those used to make the rest of the fabric. With woven fabrics that use a different weave or thread to create finished edges, the selvage is often discarded before individual pattern pieces of a garment are seamed together.
One type of woven fabric that incorporates these finished edges is called selvage denim, which is a type of denim with a distinct self-finished edge that is often used for making jeans. Selvage denim is woven by hand using a shuttle loom, which is a type of loom that stores the weft thread in an oblong tool called a shuttle. Fabric woven on this type of loom is narrower than fabric woven on looms that do not use a shuttle, so makers of jeans must compensate for the lack of width by using extra length. The most economical way to make a pair of jeans with this type of denim is to use as much of the woven fabric as possible, including the self-finished edges, which usually fall on the outer leg seams of a finished pair of jeans.
In knitting, selvages are created by using a different stitch pattern for the stitches closest to the edges of the knit fabric. This creates edges that are firm, neat, and will not unravel. A knit selvage is often used to facilitate seaming, although it can also be used to make a finished edge on a piece that does not require seams, such as a scarf. This type of finished edge is useful for securing the sides of knit pieces made from slick, smooth yarns that may slide out of place due to wear or repeated washing, such as silk or bamboo yarns.