General Terminology, Residential Sector, Commercial Buildings Sector, Transportation Sector, Industrial Sector:
http://www.eia.doe.gov/emeu/efficiency/ee_gloss.htm

Energy Intensity Indicators
http://www1.eere.energy.gov/ba/pba/intensityindicators/trend_definitions.html

Green buildings:
http://www.masstech.org/cleanenergy/energy/glossaryefficiency.htm

Energy Efficiency Terms
http://www.eeph.org.uk/resource/glossary/

Energy efficiency retrofits  
Modifications to lighting, heating, water heating, ventilating, air conditioning systems and auxiliary equipment, or modifications to building envelopes to reduce energy consumption and costs. They include capital investments and modifications to building operation and maintenance practices (this includes a lighting retrofit).
http://www.ec.gc.ca/cppic/en/glossary.cfm?view=details&id=91

Energy Glossary
http://www.energy.ca.gov/glossary/glossary-e.html

Clean Energy
http://www.epa.gov/cleanenergy/energy-and-you/glossary.html

Energy Efficiency Opportunities
http://www.energyefficiencyopportunities.gov.au/index.cfm?event=object.showContent&objectID=A7A21C39-D56D-2C65-A841E2C620353876

Heating & Cooling glossary
http://www.trane.com/Residential/Glossary.aspx

Energy Terms
http://www.sustainableenergycoalition.org/component/option,com_glossary/Itemid,33/catid,17/func,view/term,ENERGY%20EFFICIENCY/