Ghosting is a condition where particulate matter sticks to walls, carpets, and other surfaces due to air movement, concentrated particulate matter in the air, and/or electrical attraction of particles and surfaces. Many times you may see this in carpet as the bottom of baseboards in homes 20 yrs old and older (at least that’s the age in my region, Ohio). This is caused by HVAC systems that instead of fully enclosing the HVAC ducts, they simply “pan off” the floor joists and/or stud cavities with sheet metal and let the air flow through the cavity, causing leakage which after years will show up as ghosting in the carpet.