Bone marrow is the flexible tissue in the interior of bones.
The bone marrow produces the cellular elements of the blood — including platelets, red blood cells, and white blood cells — in a process known as hematopoiesis.
Bone marrow examination refers to the pathologic analysis of samples of bone marrow obtained by bone marrow biopsy (removal of bone with the marrow inside) and bone marrow aspiration (removes a small amount of bone marrow fluid and cells through a needle inserted into a bone).

Bone marrow examination is used in the diagnosis of a number of conditions, including: leukemia, multiple myeloma, lymphoma, anemia, pancytopenia, chromosome problems, marrow cultures, cancer staging, etc.
The role of bone marrow aspiration and biopsy is to obtain information regarding hematopoiesis.

Adapted from Wikipedia, the free encyclopedia. Internet. Accessed on May 27, 2016.