What is the formal definition of quasi static process?
I am accustomed with it a bit intuitively, i want to know the formal definition of this. At some source I found the definition of somewhat reversible adiabatic process which somehow also defines quasi static process
"def. 8: Adiabatic process is a process by which the system parameters change so slowly that the characteristic time of changing is much longer than the period of the slowest mode of natural oscillations; also, there should be no dissipative processes (where mechanical energy is converted to heat), e.g. friction. In the case of gases, this means that the speed of the container walls needs to be much smaller than the speed of sound, and also there should be no external heat supply. "
Basically the emphasized text defines quasi static process, Now my questions:
What is characteristic time of a process?
What is mode of natural oscillation of a system?
So what is formal definition of quasi static process?