Appendix A: Conditions
Player's Handbook · chapter
Conditions alter a creature's capabilities in a variety of ways and can arise as a result of a power, a class feature, a monster's attack, or other effect. Most conditions, such as blinded, are impairments, but a few, such as invisible, can be advantageous.
A condition lasts either until it is countered (the prone condition is countered by standing up, for example) or for a duration specified by the effect that imposed the condition.
If multiple effects impose the same condition on a creature, each instance of the condition has its own duration, but the condition's effects don't get worse. A creature either has a condition or doesn't.
The following definitions specify what happens to a creature while it is subjected to a condition.