Building Council (USGBC) created LEED as a rating system for green building. Green building refers to the design, construction, and operation of buildings in an environmentally friendly way.
LEED promotes a whole-building approach to sustainability by recognizing performance in five key areas of human and environmental health: sustainable site development, water savings, energy efficiency, materials selection, and indoor environmental quality.
The rating system is specific to the type of project being worked on. Some of the specific programs are LEED-New Construction, LEED-Existing Buildings, LEED-Commercial Interiors, LEED-Core and Shell, LEED-Homes, LEED-Neighborhood Development, LEED-Schools.
Certification levels within the systems are:
Minimum points: Certified
Second highest points: Silver
Third highest points: Gold
Fourth-maximum points: Platinum
For more information check out the USGBC website.