Slalom is a Norwegian word, referring to a sloping track. I'm pretty sure it's always referred to skiing, it's just that some other people thought it would be a good idea to use it to describe other types of zigzagging.
So far, I've never heard the Norwegians talk about slalom in reference to driving.
It refers to zig-zagging around a set of obstacles. It's common in different US of A states, or other countries to do it as part of a driver's test, or when testing cars or car design, it's used to test steering.
Imagine a row of obstacles (usually traffic cones) with large caps in between. The goal is to drive on one side of the first, and then the other side of the next. You're passing between each set of obstacles. That's a slalom.
Here's a picture if you're still having issues imagining it: http://imgur.com/a/CGEWL