From Bulbapedia, the community-driven Pokémon encyclopedia.
Flinching is when a Pokémon becomes unable to attack for one turn. The following moves may cause their targets to flinch, but only if the user of the moves hits first.
Prior to Generation V, if Razor Fang or King's Rock has an effect on a move, there is a
p + (1 - p) * 0.1 chance of causing flinching, where p is the chance of flinching, when using a move on this list and holding the King's Rock or Razor Fang. The doubling effect of Serene Grace will activate before the King's Rock or Razor Fang boost. Generation V changed it so that the chance of flinching by items and moves does not stack.