This refers to the effects of Stun, Slow, Burn, and Poison.
Hitting a burned enemy, for example, will cause nearby enemies to also burn, the same applies to Stun and Slow.
In the case of Poison, it applies only one poison stack and does not apply all the stacks from the target.
Multiple effects can be transferred at the same time (if the target is burned and poisoned, both effects will spread).