Myeloid cells are a diverse group of cells that originate from the bone marrow and play a crucial role in the body's immune response. These cells include granulocytes (neutrophils, eosinophils, and basophils), monocytes, macrophages, and dendritic cells. They are essential for innate immunity and are involved in various functions such as phagocytosis, antigen presentation, and cytokine production.