Xylene (C₆H₄(CH₃)₂):  Colorless liquid of the aromatic group of hydrocarbons made the catalytic reforming of certain naphthenic petroleum fractions. Used as high-octane motor and aviation gasoline blending agents, solvents, chemical intermediates. Isomers are metaxylene, orthoxylene, paraxylene.

Yellowcake:  A natural uranium concentrate that takes its name from its color and texture. Yellowcake typically contains 70 to 90 percent U₃O₈ (uranium oxide) by weight. It is used as feedstock for uranium fuel enrichment and fuel pellet fabrication.

Zero Energy Building (ZEB):  An energy-efficient building where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy.