A distorted board is almost always a sawn board from a sawmill. The distortion, which occurs during drying, may take any of the four forms demonstrated in the images below. The longer and wider the board, the more obvious any distortion, but when cut into furniture parts, the distortion can usually be overcome during the stock preparation stage.
A twisted board usually presents the worst salvage problem. Provided MC is in the 8% to 10% range, if you leave the sawn parts to stabilize in a dry shop for a couple of weeks before preparation, they will normally remain flat after preparation.