The mixed state in quantum mechanics is the statistical ensemble of the pure states.

The pure state of a quantum system is usually denoted by the vector ket with the unit length.

A coherent state is a quantum state that is a superposition of different number states. It represents a well-defined classical-like state of an oscillator in quantum mechanics, with a fixed phase relationship among different energy levels and minimum uncertainty in position and momentum measurements. These states are important in quantum optics and quantum information processing due to their special properties.

A W state is a quantum state of three cubits which represents a specific type of multipartite entanglement.

Wavelengths of absorbed or emitted photons

Every line in a line spectrum is caused by a transition, from one quantum state to another quantum state, involving electrons.