Military Acronym - Transporter/Erector/Launcher, from the three functions a TEL performs on ballistic missiles. In almost any picture of a parade down the middle of Red Square in the good old USSR, you will see TELs loaded down with SRBMs or MRBMs or even ICBMs. Thanks to CNN, most Americans are familiar enough with the MAZ-543 TEL... only they think of it--the whole thing--as a "SCUD". The SCUD is the missile on the back. The awesome four-axle MAZ-543 is the TEL underneath.
The transporting part is easy, and most (I believe all) TELs carry their payload in the horizontal position. Erecting a missile is a little harder, and requires a really solid secondary diesel engine on board to run the hydraulics. These are tied in to the strongback, the metal truss which holds the missile or its launch canister rigid and keeps it from bending under its own weight. Once the missile is tilted to the vertical, launching it is trivially easy. A TEL can "scoot" away from the launch signature of its payload quickly, and reload back home, many miles away, making it a fabulous strategic (and tactical) asset if you plan on using ballistic missiles in a shooting war.
Last but not least, TELs aren't all trucks. The Russian SS-24 is rail-mobile, and there were plans to make the Peacekeeper rail-mobile to keep up with the Zhonesky's. Minus the missiles, most road-mobile TELs are some of the most durable, badass trucks ever built. To a MAZ, the expression "Ford Tough" means jack.