The National Soil Erosion Research Laboratory
Soil texture refers to the composition of the soil in terms of the amounts of small (clays), medium (silts), and large (sands) size particles. The primary particles of sand, silt, and clay make up the inorganic solid phase of the soil. These particles often become aggregated together with each other and other parts of the soil, most importantly soil organic matter.
In general, the size of soil particles and their spacing determine how much water can flow through the soil. The larger the spacing, or pore size, the greater the infiltration rate. Thus, sandy soils will have high infiltration rates because pore sizes are large and there are no finer materials to block the pores.