Conditions are states imposed on creatures by various effects, including powers, traps, and the environment. A condition is usually temporary, imposing a penalty, a vulnerability, a hindrance, or a combination of effects.
Duration: The effect that imposes a condition on a creature specifies how long the condition lasts. For instance, a cleric might use an attack power that makes its target blinded (save ends). However, some conditions have built-in rules for when they end. For instance, the prone condition ends on a character who stands up, and the dying condition ends on a character who regains hit points.
No Degrees of Effect: Conditions don’t have degrees of effect; either a creature has a condition, or it doesn’t. Putting the same condition on a creature more than once doesn’t change the condition’s effect on that creature. For instance, if a weakened creature is subjected to the weakened condition again, the creature still deals half damage, not one-quarter damage.
Published in Rules Compendium, page(s) 229.