"Horizontal planks" refers to long, flat pieces of wood or other materials that are positioned parallel to the ground or floor, running from left to right or right to left. Full definition
I found another great DIY horizontal plank walls tutorial. (theinspiredroom.net)
I just added horizontal planks to the wall above our fireplace — your previous home's fireplace and mantel were our inspiration! (theletteredcottage.net)
I voted horizontal cause I LOVED loved LOVED your old house horizontal planks. (theletteredcottage.net)