Osteoclasts are multinucleated cells. The one shown here has about 8 nuclei, not a very unusual situation.
Osteoclasts arise by the fusion of mononuclear precursors.
Syncytial cells similar in nature are found in other locations. Osteoclasts have the capacity to secrete hydrogen ions and pump them outside into the space near the bone. This lowers the local pH, and dissolves the mineral matrix. The osteoclast's other enzymes take care of the organic material. This, too, is in keeping with the nature of syncytia.