An airtight canister in which a cold launched missile is stored to protect it from the elements, and from which it is eventually launched. Usually designed with quite a bit of care, a launch canister usually has an external data and power port to run all the cool features inside, like
Well, no launch canister has all of those. But when you use a launch canister, your options for how to fire the missile in question expand greatly. You can slide the canister into a missile silo--the process looks extremely sexual, but then any process involving missiles has sexual connotations. When you use a canister to sheath the mighty ICBM before placing it in the silo, then after the launch, cleanup is much easier. Just remove the hot, dirty canister and dispose of it properly! No hard feelings, no wet spot.
If silos aren't your style, you can also mount the launch canister on a road- or rail-mobile TEL, giving it the mobility that every seventy-ton steel penis yearns for. Drive around the scenic Iraqi countryside in your studly MAZ, threatening Kurds and CNN reporters with your mighty protruding technological transfer.
What's that you say? Saddam Hussein's SCUDs don't use a launch canister? I always knew he was a dirty bugger, but come on! Even the Soviet Union had the sense to protect their assets. If he's lucky, all he'll get is rust spots. If he's not lucky, the hydraulics on his TEL could get weathered, and the transporter-erector-launcher will eventually experience an erectile dysfunction.