In classical mechanics state of a system (or body) refers to its condition at a particular moment of time; thus the terms initial state, reference state etc.

State is sometimes used as a synonym for phase of matter.

State (computer science)

In physics, the term state is used in several related senses, each of which expresses something about the way a physical system is.

In thermodynamics/statistical mechanics, a thermodynamic state, or more precisely, a macrostate, is the specification of a particular combination of physical properties (e.g. temperature, volume, pressure, etc). For example, an equation of state describes the relationship between macrostates of the system.

In the study of dynamical systems, a physical system is typically modeled as a differential equation. The variable in such an equation is often called the state of the system. In some cases, this coincides with the thermodynamic sense, or it may be more abstract.

In quantum mechanics, the state vector of an object contains information about the way that object currently is. For example, the state vector Ψ of a spinless free particle moving on a line, also called particle's wavefunction, is represented by <math>e^{i(kx - \omega t)}</math>. In this formalism, the letter t denotes a moment in time, and the letter x denotes the particle's position at moment in time t. The parameters k, and ω, are related to the speed, and mass of the particle. Thus, a particle's state vector contains information about the position, mass, and speed of the particle. In general, one can always describe a quantum mechanical system, which could consist of more than one particle, by its state vector. It should be noted that the concept of a "state vector" has led to some confusion in physics, as is evidenced by the paradox known as Schrödinger's cat.