yard waste The part of solid waste composed of grass clippings, leaves, twigs, branches, and garden refuse.

years of potential life lost. A measure of the impact of premature mortality on a population, calculated as the sum of the differences between some predetermined minimum or desired life span and the age of death for individuals who died earlier than that predetermined age.

yeast A type of unicellular fungus that is not characterized by typical mycelia.

yellow-boy Iron oxide flocculent; usually observed as orange-yellow deposits in surface streams with excess iron content.

yield 1) The quantity of water (expressed as a rate of flow– gpm, gph, gpd, or total quantity per year– that can be collected for a given use from surface or groundwater sources. The yield may vary with the use proposed, with the plan of development, and also with economic considerations. Also see safe yield. 2) See energy yield.