Bone marrow stem cells are cells in the spongy tissue inside bones that create all your blood cells (red, white, platelets) and can develop into other cell types like bone, cartilage, and fat, making them crucial for blood cell production and regenerative medicine, used in treatments for cancers and blood disorders. There are two main types: hematopoietic stem cells (HSCs) for blood and mesenchymal stem cells (MSCs) for connective tissues, both vital for healing and therapies.