Knots are a no-no in needlepoint and should never be a permanent fixture in your canvas, unless it is meant to be part of the design.
A waste knot is a temporary knot that is used to start a length of needlepoint yarn. It is covered with stitches and clipped away after stitching, hence the term waste knot.
In this example, we will use Continental Stitch, but the same concept applies to any needlepoint stitch.
To begin, thread your needle with a length of tapestry thread. On the end of the thread furthest from the needle, make a large knot.
Next, insert your needle into the canvas 1 to 2 inches from the area you wish to begin stitching, and then bring the needle up to the right of the actual location where stitching will begin. You will now have a length of thread on the back side of the canvas.