Here's a nutshell description.
If separation between aircraft is not good on approach, to avoid a go-around, sometimes ATC will request that an aircraft S-turn. All this basically consists of is turning a little bit left and then back right again, so you're making a very lazy-looking S across the approach path. It basically reduces the speed you're closing on the runway, thereby increasing separation.
It's nothing like S-turns across a road.
Interesting point though...I don't know how many airline guys will do S-turns below 1000'AGL because most airlines I know require that the aircraft be stabilized on approach by that altitude...and I wouldn't consider an aircraft doing S-turns to be doing a "stabilized" approach.
Hope this helps