Bone marrow biopsy: The removal of a sample of bone marrow and a small amount of bone through a large needle. Two samples are taken. The first is bone marrow by aspiration (suction with a syringe). The second is a core biopsy to obtain bone marrow along with bone fibers. After the needle is removed, this solid sample is pushed out of the needle with a wire. Both samples are examined under a microscope to examine the cells and the architecture of the bone marrow.