A process by which water-saturated sediment temporarily loses strength and acts as a fluid, like when you wiggle your toes in the wet sand near the water at the beach. This effect can be caused by earthquake shaking.
And NOW, you can pat yourself on the back for learning something new about earthquakes!
P.S. Why should we worry about liquefaction? It goes without saying that Oregon’s a pretty wet place (What do you call two days of rain in Oregon? A weekend.) and our ground is soggier than most. And anything that goes in that ground, like those houses on stilts we see in the West Hills, has a good likelihood of coming straight down. Yikes.