The Leadership in Energy & Environmental Design (LEED) Green Building Rating System is the nationally accepted benchmark for the design, construction, and operation of high performance green buildings. It is a voluntary, consensus-based national rating system that promotes a whole-building approach to sustainability.
 

LEED for Homes is a rating system that promotes the design and construction of high-performance green homes. A green home uses less energy, water and natural resources; creates less waste; and is healthier and more comfortable for the occupants. Benefits of a LEED home include lower energy and water bills; reduced greenhouse gas emissions; and less exposure to mold, mildew and other indoor toxins. The net cost of owning a LEED home is comparable to that of owning a conventional home.

So there is your formal definition, but your question was- How does it benefit me?

A comprehension of the basic principles of LEED, and an understanding and following of those principles will direct the construction of your home towards Durability and Sustainability. The underlying benefits of building a durable and sustainable product are vast. I strive for durability and sustainability first and foremost, I find that energy efficiency follows along as well as indoor air quality and comfort. I think its important to understand that this is an ever evolving process. More on this latter......