> What does the "GL" designation mean?

nobody really knows ... and vw never said.

but it goes back to the semi-olden days of cars ... when the
manufacturers wanted to designate their luxo models from the plebian
grocery-carriers. ;)
L - usually meant Luxury or some form of that word - more 'stuff' than
the base models.
GL - was then Grande Luxury; more better than just the L.
GLS - was Grand Luxury Sport!! more better than L but more
sporty/racey than the GL.
GT - Grande Touring. not sport, but not luxury ... sort of comfy
trip-taking.
GTO - was Grande Touring Obligato or however you say Olbigatory in
Italian. :) it meant that at least 100 of these cars had been produced
to meet the rules of racing in certain classes under the regulations
of some european racing organizations. if you didn't build at least
100 of them, you had to race against a different bunch of folks (who
usually had lots more money and bigger engines!).

don't think i ever saw a just-G label. but there were LS, and later
the japanese started up the XL and XLS ... Xtra Luxury? :)

so basically, it's just a trim/interior/accoutrements difference
designator ....
an L might have carpet (instead of the rubber mats that were used in
the base models)
but a GL might have carpet AND leather seats AND power mirrors.
whereas a GLS would have carpet and leather seats but a manual
transmission and more hp in the engine.
a GT might have carpet and leather seats, manual transmission and more
hp, but air conditioning (as standard. already figured into the
price), and fog lights or driving lights or both.
and a GTO might have almost nothing ... since it was expected that you
were going to fit it out with your own seats and if you're racing, you
don't want/need carpet, and so on.

so it kinda works this way:
no letters - cheap car.
the more letters, the more expensive the car.
:)

simple, yes?

hope it helps. ;)
unca joel