Noun: A solution obtained by leaching or dissolving out soluble constituents from ashes, soil, etc. by percolation.
In environmental science: When I heard this word, it was used to describe the toxic run-off from rainwater flowing over landfills. The leachate formed in this way is in danger of contaminating drinking water sources if it is not properly contained and processsed.
Now that I think about it, coffee is a type of leachate. :-D One of the better leachates.
Etymology: 1930-1935. "leach" + "-ate."