Kiting is a general gaming term meaning keeping your distance to the target but moving and shooting at the same time, thus keeping the target busy trying to hit your unit. Think of a person holding a kite on a string. The kite always stays the same distance away even as the person moves around.
Many of the units in Supreme Commander will fire of their own accord when an enemy is within range, even if moving. This techinque can therefore be used to gain an advantage over units with clumsier weapons.
You can also, for example, order a Cybran Galaxy battleship to patrol a section of coast. Providing radar signatures are available for targeting, the Galaxy will turn its heavy artillery on targets on the coast, while continually sailing back and forth, making it a difficult target for any enemy heavy artillery to hit.
A better example however, would be the UEF Fatboy vs Aeon Galactic Colossus. In a 1v1, the Fatboy will lose due to the GC's greater firepower and considerably greater armor, but if you KITE the Fatboy and keep it driving away from the GC as the GC chases it, the greater range of the Fatboy will win as it will continually fire on the GC but receive no damage as it is staying too far away.
Note: The speed of the Galactic Colossus is 2.5, whereas the speed of the Fatboy is only 1.75. The means that the Galactic Colossus will most likely catch up to the Fatboy before the Fatboy's trademark Gauss Cannons can destroy the Galactic Colossus. Also, due to the fragility of the Fatboy, the GC only has to get within range of the Fatboy to do extreme damage. [The fatboy has a cumulative health - shield included - of 32,500, whereas the GC has a health of 99,999].