Sluck is the combination of snow and sleet that accumulates underneath the wheel wells and bumpers of semi-trailer trucks on the interstate during winter storms that always seem to let loose as you are passing them going 60 MPH.
Royce: Well, I'm glad the snowstorm seems to have let up. The road is clear enough to drive a little faster now.
Tom: Yeah we should be able to make it to Chicagopretty close to when we thought we would.
(Car passes a Semi trailer truck and "splat")
Royce: Wow, that was a lot of sluck from that semi. I'm glad the wipers are still working.