  The concept of quantum-mechanical nematic order, which is important in
systems such as superconductors, is based on an analogy to classical liquid
crystals, where order parameters are obtained through orientational expansions.
We generalize this method to quantum mechanics based on an expansion of Wigner
functions. This provides a unified framework applicable to arbitrary quantum
systems. The formalism is demonstrated for the cases of Fermi liquids and spin
systems. Moreover, we derive new order parameters for molecular systems, which
cannot be properly described with the usual nematic tensors.
