The original CJ stood for Civilian Jeep - They were numbered CJ 2A CJ5 etc. That lasted from the begenning to the late 80's when they put out the YJ. I have no idea what the rest stand for YJ, TJ, JK, but the first ment Civilian.
It started as an alphabetical way to denote the newer models. For instance the military jeep started as a MA meaning M=military A=the first model. then going to MB same deal M=military B=second model.
GP came along for fords version G= goverment issue and P=80" wheelbase recon vehicle (cuz ford always has to be complicated)
Every jeep for the first little while was consecutive even the prototypes that did not make it to mass production. CJ is like stated above C=civilian J=jeep. some of them never made it to the public such as CJ1 CJ4(1 prototype exists of the CJ4)
then somewhere along the lines they just started using random letters without any real name other than the letter YJ TJ with the only recent exception being the LJ L=lenthened
postal jeeps where DJ d=dispatcher jeep and most if not all where 2wd, FC= forward control
these models the letters do not stand for a word just a model designation
YJ=WRANGLER, TJ=WRANGLER, ZJ=1STGRAND CHEROKEE WJ=2ND GRAND CHEROKEE WK=3RD GRAND CHEROKEE MJ=COMANCHEE PICKUP KJ= LIBERTY XJ= CHEROKEE VJ=JEEPSTER SJ=FULLSIZE CHEROKEES J-TRUCK=THE FULLSIZE TRUCKS.
When the YJs came out, the CJ drivers all bashed them.
When the TJs came out, the YJ drivers all bashed them.
When the JKs came out, everyone bashed them.
I sense a trend here. I don't care for the styling changes in the JK, but they seem to me to be every bit as much of a jeep as the others. In a few years, whoever winds up owning the jeep line will have a new model, and we can all bash that too, even the JKers.