A neji (pronounced /nɛdʒi/ "nedgy"; for "near-equal JI") is a circulating temperament which approximates an equal tuning dividing a JI equave with a subset of a mode of the harmonic series. It is often informally used for a harmonic series approximation of any non-JI scale, e.g. "neji Lydian".
In Zhea Erose's primodality theory, nejis can be used to explore a prime family (see primodality), while keeping the transposability, scale structures, rank-2 harmonic theory, notation, etc. associated with that edo. (The neji's denominator need not be prime but primes may be preferred for sake of minimizing lower-complexity intervals. Zhea often uses semiprimes pq.) Zhea Erose's theory also deals with modulations between different prime families, and combining different prime families into one scale.
Nejis are a specific type of detempering. Detempering in general does not require the rational pitch replacements to all be part of the same harmonic series.