Soils are roughly divided into three categories, determined by the diameter of the particles that make it up: sand (fine, like at the beach), loam (very fine, so grains are just perceptible between your fingers), and clay (finest, slippery when wet). The size of particles that make up soil determine its water capacity and cation exchange capacity, both of which are important in determining the behavior of the largest and most important part of good vineyards: their roots. If we go so far to say as the non-human gut biome we all live with is a part of us, the soil around the roots are just as much a part of the vine.
Soils with healthy populations of beneficial microorganisms and mycorrhizal fungi are key to high quality fruit and the wine made from it.
Soil can be a generous term for vineyards in their most extreme examples, like the steep slate slopes of the Mosel or Priorat, where vinous ecosystems eke a living from rock dust between slabs of stone.