A (macroscopic) classical state is due to the decoherence of quantum states of a lot of particles.

A quantum state is a quantum eigenstate or a superposition of quantum eigenstates. 

a classical state = a macroscopic definite state

a quantum eigenstate = a microscopic definite state

a definite state = a state whose measurement result can be predicted with 100% certainty

— Me@2013.06.16

2013.06.17 Monday (c) All rights reserved by ACHK