  We discuss the formation mechanisms and structure of the superdense dark
matter clumps (SDMC) and ultracompact minihaloes (UCMH), outlining the
differences between these types of DM objects. We define as SDMC the
gravitationally bounded DM objects which have come into virial equilibrium at
the radiation-dominated (RD) stage of the universe evolution. Such objects can
be formed from the isocurvature (entropy) density perturbations or from the
peaks in the spectrum of curvature (adiabatic) perturbation. The axion
miniclusters (Kolb and Tkachev 1994) are the example of the former model. The
system of central compact mass (e. g. in the form of SDMC or primordial black
hole (PBH)) with the outer DM envelope formed in the process of secondary
accretion we refer to as UCMH. Therefore, the SDMC can serve as the seed for
the UCMH in some scenarios. Recently, the SDMC and UCMH were considered in the
many works, and we try to systematize them here. We consider also the effect of
asphericity of the initial density perturbation in the gravitational evolution,
which decreases the SDMC amount and, as the result, suppresses the gamma-ray
signal from DM annihilation.
