Percolation threshold

Percolation threshold is a special point or number that tells us when a liquid or gas can start running through a material. It's like a limit. Imagine you have a sponge, when you pour liquid onto the sponge it will start to soak up the liquid. After a while the sponge will become completely soaked, and then if you keep pouring, some of the liquid will start to come out of the sponge. The point where the liquid starts to come out of the sponge is the percolation threshold.