While a launch vehicle is being fueled on the launch pad, what is holding it up? Surely not all that weight is being held up by the engine nozzles. What parts of the launch vehicle are supporting its entire weight prior to ignition? Is there a term for this? I am sure it's different for each vehicle, but any example would be great.
The platform holding launch vehicle is called "launch pedestal" or "пусковой стол" or "стартовый стол" (in russian). Usually there are special "Hold-Down Arms" or "support arms" ("опоры пускового стола") to hold rocket.
1.. Proton is supported at bottom. There is launch pedestal model: http://www.cardmodels-r.narod.ru/html/Proton-LP1.htm
In the middle there is round interface plane "блок разъемов пускового стола" (with electrical ports). Six white elements are top view of support arms.
Side view, arrow pointing to interface plane (actually, to position of "lift-off switch" - "контакт подъема") :
When rocket goes up, support arms will rotate and hide in the green protection cones, and interface plane will go down and protected with special doors.
There is cross-section of proton pedestal. In the middle we have interface plane, and support arms with rotation mechanism is shown in green:
Last stages of installing Proton from transport vehicle ("Установщик", 8У260) to launch pedestal:
2.. Saturn's "Hold-Down Arms and Tail Service Masts" - http://www.hq.nasa.gov/pao/History/SP-4204/ch13-4.html
The hold-down arm:
In cross-section of arm - http://www.hq.nasa.gov/pao/History/SP-4204/images/m287a.gif we can see bottom part - the "support arm" and the top "upper link" which is used as "hold-down arm" to hold down the Saturn before reaching full thrust.
3.. Saturn 1 support arm's photo: http://heroicrelics.org/ussrc/s-i-bl-i-support-arm/index.html and hold down arms: http://heroicrelics.org/msfc/s-i-bl-i-holddown-arm/index.html
Schematics of LC-34 Launch pad http://www.hq.nasa.gov/pao/History/SP-4204/ch2-4.html
4.. NASA’s Space Launch System (SLS) - http://www.nasaspaceflight.com/2012/11/nasa-sls-mobile-launcher-umbilical-plans/
Here we can see at right 3 Vehicle Support Posts of nearest booster. There are 4 support posts for each booster, and there are two boosters.
Most rockets are supported at the base of the fuselage. This is generally the location where the engine is connected to the framework of the rocket. EG The base of the STS SRBs are connected to the pad with 4 explosive bolts. They blow a few ms after the ignition of the boosters.
An exception is the Soyuz (R-7 and its descendants) which are actually suspended over the pad by 4 large 'arms'. These lock into place after erection and are released during launch.