From 3GPP TS 37340, V15.0.0, below abbreviations are given
DC - Intra EUTRA DC
MR-DC - Multi-RAT DC
EN-DC - E-UTRA - NR DC
NE-DC - NR - E-UTRA DC
NGEN-DC - NG-RAN E-UTRA-NR DC
Let's take a detailed look into them.
DC is a legacy term and known from LTE context.
MR-DC is more of generic term, I guess, to give bit more flexibility to expand the DC to 5G.
EN-DC, as I understand, architecture is based on E-UTRAN where it houses both eNB and gNB with EPC as the Core Network. In this gNB is called as en-gNB (I think denotes EN-DC implicitly and gNB supports inter working with eNB)
NE-DC contains NG-RAN with gNB and eNBs. Here, eNBs are called as ng-eNBs (Next Gen eNBs - supports inter working with gNB) and gNB is connected to the 5GC (5G Core).
NGEN-DC contains NG-RAN with ng-eNB and gNBs. Here ng-eNB is connected to 5GC.
For my understanding, I have categorized the above info as below.
