Question: In quantum mechanics Step potential, each term of the solution can be interpreted as what?
About the article "Quantum mechanics", section "Step potential".

Candidate passages:
The potential in this case is given by:
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The solutions are superpositions of left- and right-moving waves:
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where the wave vectors are related to the energy via
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with coefficients A and B determined from the boundary conditions and by imposing a continuous derivative on the solution.
Each term of the solution can be interpreted as an incident, reflected, or transmitted component of the wave, allowing the calculation of transmission and reflection coefficients.
Notably, in contrast to classical mechanics, incident particles with energies greater than the potential step are partially reflected.
The quantum harmonic oscillator is the quantum-mechanical analog of the classical harmonic oscillator.
Because an arbitrary potential can usually be approximated as a harmonic potential at the vicinity of a stable equilibrium point, it is one of the most important model systems in quantum mechanics.
Furthermore, it is one of the few quantum-mechanical systems for which an exact, analytical solution is known. 
According to Krivchenkov, the intents to "interpret" quantum mechanics in terms of classical mechanics have no more sense than interpretation of heliocentric cosmological system in terms of geocentric system.
Only the old tradition forced the physicists to discuss the so-called Copenhagen interpretation of quantum mechanics.
Quantum mechanics is completely deterministic systems, where any event always has a cause and any cause always has an effect.
However, some quantum mechanical systems are complicated, so we have to describe them classically (quasi-classically, semi-classically, pseudo-classically, ...).
Then, immediately, probability appears, because classical mechanics cannot interpret events in a deterministic way.
An intermediate step is provided by the formalism of the density matrix, that allows us to keep some quantum mechanical properties in the classical description; however, such a description is not complete and it is just a compromise between the deterministic description of too complicated a system and wishes to make any (at least probabilistic) predictions.
As an example of the superiority of quantum mechanics, Krivchenkov usually cited the 3-body problem.
The 2-body Kepler problem has an analytic ("exact") solution, which is periodic.
The quantum-mechanical analogy corresponds to the Hydrogen atom, which also has an analytic ("exact") solution in closed form, described with the Coulomb wave function.
The addition of a third particle Helium atom still admits analytic estimates that can be performed by a 3rd-grade student.
However, the classical analogy becomes so complicated that it is not even included in a university course of astronomy.
In such a way, it is classical mechanics that could in some sense be interpreted in terms of quantum mechanics (the correspondence principle).
By itself, quantum mechanics is a self-consistent deterministic theory that does not need any interpretation. 
The Heaviside step potential mainly serves as an exercise in introductory quantum mechanics, as the solution requires understanding of a variety of quantum mechanical concepts: wavefunction normalization, continuity, incident/reflection/transmission amplitudes, and probabilities.
A similar problem to the one considered appears in the physics of normal-metal superconductor interfaces.
Quasiparticles are scattered at the pair potential which in the simplest model may be assumed to have a step-like shape.
The solution of the Bogoliubov-de Gennes equation resembles that of the discussed Heaviside-step potential.
In the superconductor normal-metal case this gives rise to Andreev reflection. 
In advanced topics such as quantum mechanics and relativity it is often easier to work with a potential formulation of electrodynamics rather than in terms of the electric and magnetic fields.
In this representation, the "vector potential" , and the scalar potential , are defined such that: formula_34 formula_35 The vector potential may be interpreted as a "generalized potential momentum per unit charge" just as is interpreted as a "generalized potential energy per unit charge".
Maxwell's equations when expressed in terms of the potentials can be cast into a form that agrees with special relativity with little effort.
In relativity together with forms the four-potential, analogous to the four-momentum that combines the momentum and energy of a particle.
Using the four potential instead of the electromagnetic tensor has the advantage of being much simpler—and it can be easily modified to work with quantum mechanics.