Junk is anything that can't become reshaped into useful scrap. Dead computer motherboards, burned out power supplies, iron pipe that I've torn out of the house in the ongoing process of restoring its bones from 2 apartments (happened in 1932) back into a functional maintainable single-family home. Happily, most junk does not go to the landfill, it goes into one recycling stream or another. (Though I have not found a recycling stream that will accept crumbled 130 year-old plaster.)
Waste is a verb. Waste is stashing your previous computer in the back of the closet or on an office shelf. Where it lingers over the period of time where it might be useful, to somebody else, in another role. If enough time passes, it becomes junk, and is only useful as parts to be separated for recycling.
So BRING OUT YOUR DEAD! (...to be continued)