A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter.The term is sometimes used for larger particles, up to 500 nm,[citation needed] or fibers and tubes that are less than 100 nm in only two directions. At the lowest range, metal particles smaller than 1 nm are usually called atom clusters instead.
Nanoparticles are usually distinguished from microparticles(1-1000 µm), "fine particles" (sized between 100 and 2500 nm=, and "coarse particles" (ranging from 2500 to 10,000 nm), because there smaller size drives very different physical or chemical properties, like colloidal properties and optical or electric properties.