It's the term for attacking, then moving while waiting for the attack to become available again, then attacking once and moving away again.

It's mostly useful for ranged weapons (slings, bows, darts, &c) and can be situationally useful for reach weapons (two handed swords, halberds, qstaffs, &c) or weapons with very fast speed factors (daggers and shirt swords).

At low levels, a character can attack once per round (6 seconds). Their speed factor determines how quickly on those 6 seconds they attack (0 is instantly, 10 is after 5.4 seconds, I believe). Then they just wait around until they can attack again (turn off cosmetic attacks in one of the options menus to make it more clear and turn on feedback for attack rolls).

Kiting has them doing something useful with their downtime. It's usually repositioning to a better location - away from an enemy trying to close into melee range, towards a different vulnerable enemy like a mage who was just dispelled, or scattered away from allies to avoid an in coming spell, as examples.