Working a cutting edge into the rising direction of the wood fibers rather than laying them flat. This action lifts and tears the wood fibers instead of shearing them cleanly, resulting in a rough, splintered surface known as tear-out. Machining in this direction requires shallow cuts and sharp tools to minimize surface damage.
Heard on the job
You're feeding that board against the grain, so flip it end for end before the planer chews it up.
Insider tip
Always run your hand over the board to feel the grain direction. Smooth means you are going with it, rough means against.