The phrase "to have an undercoat" means to have a layer of fur or hair beneath the outer layer. It is usually used to describe animals, like cats or dogs, that have a thick layer of fur close to their skin to help keep them warm.
Sentences with «to have an undercoat»
Long coat German Shepherds don't have undercoats which makes their coats nonresistant to water if they are to get wet. (waycooldogs.com)
Cats have an undercoat of soft fluffy fur and a topcoat of coarser fur which helps to fend off wind and rain. (laurelwoodvets.com)
Meaning that the dog dosen't have an undercoat which is why the Yorkie does not shed. (elvisyorkshireterrier.com)