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R-parity is the multiplicative number $R_p=(-1{)}^{3(B-L)+2s}$, where $B$ is baryon number, $L$ is lepton number and $s$ is spin. Standard Model particles are even and their superpartners are odd.

If conserved, an initially even state produces an even number of odd states, and the lightest odd state is stable. A neutral stable state may escape a detector and give missing transverse momentum. Stability alone does not establish its cosmological relic abundance.^[ref]

Soft supersymmetry breaking adds a restricted set of dimensionful interactions to an otherwise supersymmetric action. Examples include gaugino masses and scalar field squared masses. Their ultraviolet behavior preserves the absence of the new quadratic divergences that generic explicit supersymmetry breaking can introduce.

Soft terms split partner masses, making the supersymmetric mass degeneracy inapplicable to the broken spectrum. They can still cause finite and logarithmic sensitivity to large partner masses, so softness does not make every choice natural.^[ref]