Telcordia "Common Language Standards" abbreviations for switch equipment types as used in various industry documents, mostly LEC and Telcordia documentation...

The DM[x] range of Telcordia Common Language standards abbreviations is typically for something in the Nortel DMS family of switches.

The DMO (and that's a letter 'O' (oh), not a '0' zero) refers to a Nortel DMS-10 "Host Switching Office". However, I don't really know how this really differs from 'DMT' which simply refers to a Nortel DMS-10.
A Nortel DMS-10 Remote Equipment Module is abbreviated as 'DLM'.
A Nortel DMS-10-S (small???) is abbreviated as 'DMS'
DMS-100's are DMH, the 'H' most likely referring to "Hundered"
A Nortel DMS-10 Satellite Switching Office is abbreviated as 'DSF'.

Of course, not all telcos entering their data into the Telcordia CLONES database or Telcordia-TRA database really enter the most precise abbreviations for equipment type. Thus you will find widely variances in preciseness/etc.

NOTE that the three character "switch equipment type abbreviations" that I have referred to above are NOT the same as the final three characters of a Switch-CLLI code!