Hello. I read the textbook of the thermodynamic and it said the definition of the reversible process as "thermodynamic process which is slow enough so the system state is always infinitesimally close to the thermodynamic equilibrium (quasi-static) during the process. Such a process can always be reversed without changing the thermodynamic state of the universe". I accepted this definition in a way that "quasi-static" and "reversible" is equivalent. Is this true? Is there any process which is quasi-static but not reversible?