The general term for smoothing wood prior to applying a finish is 'abrading'. This is simply the wearing away of wood fibres by the sharp teeth of abrasive material.
Abrasive papers have abrasive particles bonded to their surface: glass paper (or sandpaper) is the cheapest abrasive paper; garnet paper is harder and better quality and used for fine finishing of furniture; silicon-carbide paper is often called wet-and-dry paper, because it can be used either way. Use it wet for removing the glaze from paint before repainting: the water acts as a lubricant and also keeps down paint dust, which may contain lead. The particles are called 'grit' and these are numbered. Generally, you work through the grades, starting with the coarsest and working through to the finer ones until the wood is smooth and there are no sanding marks.
Other methods of abrading wood include rasps and files (bars of variously shaped steel with patterns of teeth cut onto their surface), or surform tools (a combination of files and planes). Steel wool, graded by '0's - the more '0's, the finer the wool - is used with white spirit for taking the gloss off sealers and varnishes before recoating.
