ACV =  Alpha CVn var.
ACY =  Alpha Cyg var. (pulsating, small-amplitude). New in GCVS4.
AK  =  Spectral types A, F, G, & K. 
AP  =  Spectral type Ap.
ASS =  Stellar association.
B   =  Spectral type B.
BAE =  Spectral type Be & Ae.
BAR =  Barium star.
BCE =  Beta Cep var. 
BE  =  Spectral type Be.
BP  =  Spectral type Bp. 
BV  =  Hubble Photometric Star Catalog (BV photometry, ref0608). 
BY  =  BY Dra var.  New in GCVS4.
BY: =  BY Dra var. (uncertain type)
CAR =  Carbon star.
CD  =  Cepheid var. (classical Delta Cep).
CEP =  Cepheid var. (general).
CG  =  Compact galaxy.
CH  =  CH-type star.
CMC =  Carlsburg Meridian Circle Catalogue (La Palma #4-8, ref0817).
CNS =  Catalogue of Nearby Stars #3 (ref0810).
COM =  Common star.
CPM =  Common proper motion pair.
CST =  Constant (non-variable) in GCVS3.
CSV =  Catalogue of Suspected Variables (ref0816).
CV  =  Cataclysmic var. (not a GCVS3/GCVS4 class).
CW  =  W Vir var.
CWA =  W Vir var. (period over 8h).   
CWB =  W Vir var. (period under 8h).
DCE =  Delta Cep var.
DCL =  Dark cloud region (SFR). (ref0748)
DKM =  Spectral types dK & dM.
DN  =  Dwarf nova.
DSC =  Delta Scu var. 
DWF =  Dwarf star.
E   =  Eclipsing var.
E:  =  Eclipsing var.(uncertain type).
EA  =  Eclipsing var. (Algol type).
EA: =  Eclipsing var. (uncertain type).
EB  =  Eclipsing var. (Beta Lyr type).
EB: =  Eclipsing var. (uncertain type).
ELL =  Eclipsing var. (ellipsoidal type).
E/C =  Eclipsing var. (combination).
E/I =  Eclipsing var. (combination).
ELS =  Emission-line star.
EUV =  Extreme Ultraviolet Source (ref0732, etc).
EW  =  Eclipsing var. (W UMa type).
EW: =  Eclipsing var. (uncertain type).
F   =  Spectral type F.
FG  =  Spectral types F & G.
FBO =  Faint blue object.
FBS =  Faint blue star.
GAL =  Galaxy.
GCA =  Gamma Cas var. (eruptive irregular).
GM  =  Spectral type gM.
GNT =  Giant star.
H2O =  Water maser star.
HAE =  H-alpha emission star.
HB  =  Horizontal-branch star.
HDS =  Hydrogen-deficient star.
HH  =  Herbig-Haro star.
HPM =  High proper motion star.
HVS =  High velocity star. 
HYA =  Hyades star (Hanson astrometric survey, ref1005).
I   =  Irregular var. 
I:  =  Irregular var. (uncertain type).
IA  =  Irregular var. (early sp. O-A).
IB  =  Irregular var. (intermediate and late sp. F-G, K-M).
IB: =  Irregular var. (uncertain type).
IN  =  Irregular (Orion) var.
IN: =  Irregular (Orion) var. (uncertain type). 
INA =  Irregular (Orion) var. (early sp. B, A, Ae). 
INB =  Irregular (Orion) var. (intermediate and late sp. F-G, Fe-Me). 
INS =  Irregular (Orion) var. (rapid, to 1-mag). New in GCVS4.
INT =  Irregular (Orion) var. (T Tau type, sp. Fe-Me). 
IR  =  Infra-red object. 
IRA =  IRAS infra-red source.
IS  =  Irregular var. (rapid, no diffuse nebula).
IS: =  Irregular var. (uncertain type).
ISA =  Irregular var. (rapid, early sp. B-A, Ae).
ISB =  Irregular var. (rapid, intermediate and late sp. F=M, Fe-Me).
IT: =  Irregular var. (one star NPM2-15.1146 = NSV 20772, ref1100).
L   =  Slow irregular var.
L:  =  Slow irregular var. (uncertain type).
LB  =  Slow irregular var. (giants, late sp. K, M, C, S).
LB: =  Slow irregular var. (uncertain type).
LC  =  Slow irregular var. (supergiants, late sp.). 
LK  =  Lick discovery (variable or proper motion star, ref0637).
LNK =  Link star for Hubble ST and Hipparcos- Argue List (ref0578).
LUM =  Luminous star (ref0489).
M   =  Mira var.
M:  =  Mira var. (uncertain type).
MDS =  Metal deficient star.
MLS =  Metallic line star.
MSC =  Miscellaneous star (generally anonymous).
N   =  Spectral type N.
NA  =  Nova (fast).
NB  =  Nova (slow).
NC  =  Nova (very slow).
NL  =  Nova-like var.
NOV =  Nova.
O   =  Spectral type O.
OB  =  Spectral types O & B.
OBA =  Spectral types O, B, & A.
ORI =  Orion var.
PEC =  Peculiar spectral type star.
PNB =  Planetary nebula (whole neb. or central star).
PPN =  Pre-planetary nebula.
PVT =  PV Tel var. (short-per. helium supergiant Bp).  New in GCVS4.
QSO =  Quasi-Stellar Object.
R   =  Spectral type R.
RAD =  Radio source (optical component).
RCB =  R CrB var.
RED =  Red star (generally giant or dwarf K & M).  Used to avoid M (Mira type). 
RNB =  Reflection nebula (SFR, ref0967).
RR  =  RR Lyr var.
RR: =  RR Lyr var. (uncertain type).
RRA =  RR Lyr var. (RRab).
RRC =  RR Lyr var. (RRc).
RRS =  RR Lyr var. (dwarf cepheid).
RS  =  RS CVn var.
RV  =  RV Tau var. 
RV: =  RV Tau var. (uncertain type).
RVA =  RV Tau var. (constant mean brightness).
RVB =  RV Tau var. (periodically variable mean brightness).
S   =  Spectral type S.
S:  =  Spectral type S (uncertain type).
SD  =  Subdwarf (all types).
S/I =  Spectral type S (combination).
SMS =  Spectral type S/SM: MacConnell (REF0495).
SP  =  "short period" var. of unspecified type.
SR  =  Semi-regular var.
SR: =  Semi-regular var. (uncertain type).
SRA =  Semi-regular var. (sp. M,C,S, near-periodic).
SRB =  Semi-regular var. (sp. M,C,S, poor periodicity).
SRC =  Semi-regular var. (late sp., flat galaxy component).
SRD =  Semi-regular var. (sp. F,G,K, giants & supergiants).
SXP =  SX Phe var.
SYM =  Symbiotic star.
TAU =  T Tau var.
UBV =  UBV photometry star.
UG  =  U Gem var.
UG: =  U Gem var. (uncertain type).
UNI =  Unique var. (* = unique in GCVS3)
UNK =  Unknown-type var. (? = unstudied in GCVS3).
UV  =  UV Ceti var.
UV: =  UV Ceti var. (uncertain type).
UVB =  UV-bright star.
UVE =  UV-excess star.
UVN =  Flaring Orion var. (sp. Ke, Me).  New in GCVS4.
VAR =  Variable (unspecified type).
WD  =  White dwarf star.
WR  =  Wolf-Rayet star.
XM  =  X-ray variable.
XP  =  X-ray pulsar system.
XR  =  X-ray object.
YPC =  Yale Parallax Catalog #3.
YSO =  Young stellar object.
ZAN =  Z And var.
ZCA =  Z Cam var. (not a GCVS4 class- contained in U Gem).
ZZ  =  ZZ Cet var. (white dwarf).
ZZA =  ZZ Cet var. (white dwarf, sp. DA).  New in GCVS4.
ZZB =  ZZ Cet var. (white dwarf, sp. DB).  New in GCVS4.
ZZC =  ZZ Cet var. (white dwarf).          Not in GCVS4.