The study of processes based on cavitation use required a clear definition of phenomena arising in liquid at high-frequency oscillation impact upon it. For the in-depth study of the phenomena under investigation in the given work there was used a high-speed video filming. As the analysis of high-speed filming has shown after closing a bubble is divided into many pieces which, in their turn, pulse in-phase. At the same time there is observed a formation of complex bubble formations which are offered to be called clusters (Fig. 3). Bubbles formed under the influence of variable acoustic pressure and located at a small distance from each other combine. Two processes take place simultaneously – bubbles combining (coalescence) and the integration of small bubbles in larger ones under the influence of cohesion forces with the formation of general structures (coagulation). The coalescence is followed with the transition of a system in a state with lower free energy.