Thank you all for your quick responses. However, I cannot agree that this the same as a "switchback" (I didn't know what it was, but I did look it up after reading about it just now), because:

1. It is always on a wide asphalt road. The wider, the better.
2. The trick is to increase the speed while the bike is positioned horizontally towards the sides.
3. You pedal with one full right stroke when turning left, and pedal with one full left stroke when turning right - all in a quick rhytmic fashion.
4. You are standing up while doing this, supporting using the pedals as mentioned in 3.

I think the most correct term one of you mentioned could be tacking, but I couldn't find anything related to tacking with bikes - only boats.