Osteomyelitis (or OM) is infection and inflammation of the bone or bone marrow.It can be usefully subclassified on the basis of the causative organism (pyogenic bacteria or mycobacteria) and the route, duration and anatomic location of the infection.rom Wikipedia, the free encyclopedia. Osteomyelitis (or OM) is infection and inflammation of the bone or bone marrow. It can be usefully subclassified on the basis of the causative organism (pyogenic bacteria or mycobacteria) and the route, duration and anatomic location of the infection.