In quantum mechanics, an adiabatic process is an infinitely slow change in the Hamiltonian of a system. Adiabatic processes are important idealizations of "sufficiently slow" processes and bear important consequences for quantum mechanics (see adiabatic theorem).
Note that the term "adiabatic" is traditionally used in thermodynamics to describe processes without the exchange of heat between system and environment (see adiabatic process). The definition above is closer to the thermodynamical concept of a quasistatic process, and has no direct relation with heat exchange. These two different definitions can be the source of much confusion, especially when the two concepts (heat exchange and sufficiently slow processes) are present in a given problem.
See also