  Clumping in stellar winds of hot stars is a possible consequence of
radiative-acoustic instability appearing in solutions of
radiative-hydrodynamical equations. However, clumping is usually included to
stellar atmosphere modeling and radiative transfer calculations in a highly
approximate way via a global free parameter called the clumping factor. Using
different values of clumping factors many researchers succeeded to fit the
observed spectra better and to correct empirical mass loss rates. This usually
leads to a conclusion that the stellar wind is clumped. To understand how
clumping may influence theoretical predictions of mass-loss rates, different
clumping properties have to be taken into account. If clumping appears already
below the critical point, the mass-loss rates is changed.
