Braid generally refers to a woven, long, piece of narrow fabric used for decorative or weight-bearing/strengthening purposes. See also: braiding technique.
Flat cross-section braids were often used for belts, straps or trim for edging clothing. Circular or square cross-section braids were often used for draw-strings, poynts, lacing etc. Very narrow, elliptical or flat-on-one-side braids were used in couching (see below).
The braid could be made separately and stitched on later, or be made as the clothing is being made (ie made as part of the clothing, stitching it down as you make it). It could be laid down straight across the fabric (eg along the top of a stomacher), or following seams in the clothing (even concealing them), or laid in decorative loops/patterns (known generally as couching).
Some braids were also used to add strength to the edges of clothing, for example, to strengthen the seam along an edge full of buttonholes to prevent the buttons tearing the fabric.
There are a number of braiding techniques, all producing different forms of braid. The most common (in the SCA) being: