From wiki: http://en.wikipedia.org/wiki/Waste
In general, waste is any objects the holder discards, intends to discard or is required to discard is waste under the Waste Framework Directive (European Directive 75/442/EC as amended).
Solid waste is the type of waste that has a solid form when discarded. These waste will pollute air, water and land. For example, building material waste due to demolition of buildings will cause air pollution (dust particles), water pollution (metallic waste mixed with acid rain), land pollution (toxic material such as asbetosis).
Some solid waste can be recycled (such as metal cans) or decomposed (such as left-over food stuffs). Others are very difficult to treat except the landfill (to avoid air pollution).