Seam removal is the process of making a join disappear: run solvent cement into the seam, press the halves so a tiny bead of melted plastic squeezes out, wait a day, then sand the cured bead flush through rising grits. Done right, the two parts become one piece of plastic with no visible history.
The classic mistake is sanding too early — soft cement smears and the seam ghosts back. The second classic mistake is skipping grits and leaving 400-grit scratches under paint.
See it in context in our sanding & surface prep guides, or explore the tools hands-on in The Bench.