A track stand is a technique originally used by cyclists racing at a velodrome (or track, hence the name).
It is disadvantageous to be leading a tight group of cyclists in a race, as the leader has to do most of the work against air resistance, whereas those following can slipstream (draft). So many track races start with a slow period of tactical waiting, followed by a mad break for the line.
Waiting on two wheels isn't intuitively easy, but putting your feet down will drastically slow your reaction to the break, especially as track racers' feet are strapped securely to the pedals.
The track stand is a technique of remaining stationary on a bike without putting one's feet down. Here's how to try it - but be prepared to fall off! Any bike will do, but knobbly mountain bike tyres will make it a lot harder.
Firstly, practice riding really slowly. See if you can "stall" the bike for a short time whilst turning up a slope - you could use the road camber, racers use the velodrome banking. Don't use the brakes to stop, let gravity do the job. If you succeed without losing your balance, you're on the way. A track stand is simply a prolonged "stall", balancing pedal force against gravity. Simply try to increase the time you can hold the stall.
Further tricks to try:
- One-handed track stand: when you've mastered the basic track stand, try taking one hand off the handlebars.
- No-handed track stand: now take the other hand off! Sounds impossible, but on a smooth slope, I can hold a no-handed track stand until I get too tired for the very sensitive pedal pressure adjustments needed.
- Reversing: on a long slope, you should be able to ease the bike backwards by letting off the pedal pressure occasionally.
Don't learn this around traffic! You are very likely to fall off as a beginner! It's probably not wise to start learning track stands at the same time as trying clipless pedals for the first time...
However, once you have mastered the technique, it is very useful in daily riding, at traffic lights and junctions. Just be sure you are competent before using it in real life. You have been warned.