Leachate is any liquid that, in passing through matter, extracts solutes, suspended solids or any other component of the material through which it has passed.
Leachate is a widely used term in the environmental sciences where it has the specific meaning of a liquid that has dissolved or entrained environmentally harmful substances which may then enter the environment. It is most commonly used in the context of land-filling of putrescible or industrial waste.
In the narrow environmental context leachate is therefore any liquid material that drains from land or stockpiled material and contains significantly elevated concentrations of undesirable material derived from the material that it has passed through.
Read more about Leachate: Landfill Leachate, Environmental Impact, Problems and Failures, Other Types of Leachate