The phrase "loose undercoat" refers to a layer of fur or hair that is fluffy and not tightly attached to the animal's body. This undercoat helps the animal stay warm in cold temperatures by providing insulation. Full definition
It is designed to easily catch and remove loose undercoat hair. (cat-health-guide.org)
So, that's the reason why you find shed hair all over — dogs have tons of loose undercoat hair that ordinary combs can't actually reach. (topdogtips.com)
A safe, unique method to remove loose undercoat on dogs of any coat type using specific brushing techniques and products designed to reduce shedding (barknbubblesdogwash.com)