Refers to the two side edges of any woven fabric, where the wefts reach the end warps, loop around them and then return back to the other side. The last centimetre or so of warp threads are often denser so they can take the tension and keep the fabric taut and true once it leaves the loom.
Selvedges of unprinted textiles can be decorative features in their own right, there is no reason to hide them. Many are woven with a thin line of contrast colour, such as red-edge linen; good selvedges can be turned to the front of unlined projects, or left as they are.
Printed cloths have useful information and colour keys printed along the selvedges, including the name of the print, the printer’s name, the colour codes *, washing instructions and sometimes the date and matching points. On light background fabrics, the selvedges should be trimmed away before making up so that the writing doesn’t show through to the finished project.
Selvedges can be so tight that they cause ruckles or tension along the edges, usually the result of a finishing process, in which case snip along the edge making small diagonal cuts until the selvedge lies flat. This ensures the fibres don’t fray subsequently. You can also trim it away all together, just so long as the cloth doesn’t unravel.
* these colour codings can be a very useful aid for paint matching and choosing other materials