Waste Canvas is a temporary canvas commonly used in Cross Stitch, but can calso be used in Needlepoint.
This canvas is loosly woven and is marked by blue lines to help you keep count of your stitches. The spacing of the blue lines depends on the count of the canvas. For example, 12-holes per inch canvas has a blue line spaced every 12 holes, and 10-holes per inch has a blue line spaced every 10 holes.
Waste Canvas is used when you wish to work needlepoint upon another fabric, and acts as a guide for stitching. Waste canvas is attached to the other fabric by pinning or basting. Next, the design is worked through both layers - the canvas and the ynderlying fabric.
Once the stitching is complete, the Waste Canvas is removed by carefully pulling out and discarding the canvas threads.
Waste Canvas is sold in pre-cut packages at most craft and sewing stores.