Definition: When you wind, or wind on, your beadwork, you move it down on your loom. You'll need to wind your beadwork when you use a fixed frame loom that is not long enough to accommodate your entire design within its two warp bars.
For example, if you want to stitch an eight-inch bracelet band, but your loom is only seven inches long, you'll need to wind on in order to complete your design. You'll also need to wind on when your method of finishing off (finishing the ends of your beadwork) requires more space, or longer warp threads, than your loom can otherwise accommodate.
That commonly occurs when you make a bracelet band and plan to weave-in all of your warp threads. In that case, the unbeaded warp threads need to be long enough on both ends of your beadwork that you can thread each one onto a needle and weave it into the beadwork.
In order to wind on with most basic bead looms, you need to use a special technique for warping your loom.