The soft, spongy tissue inside bones that produces blood cells through a process called hematopoiesis. It contains stem cells that differentiate into red blood cells, white blood cells, and platelets.
From Old English 'ban' meaning bone and 'mearh' meaning marrow, with roots tracing back to Proto-Germanic. The term has been used since ancient times, though the marrow's blood-forming function wasn't discovered until the 19th century.
Bone marrow is like the body's hidden blood factory, churning out about 200 billion red blood cells daily! There are two types: red marrow that makes blood cells and yellow marrow that's mostly fat - as we age, much of our red marrow converts to yellow marrow.
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